Bridged element for detection of a target substance

ABSTRACT

Physical changes resulting from an association between a template molecule and a target molecule are detected by monitoring changes in the template molecule. Exemplary changes include a change in a physical dimension or stiffness of the template molecule, a change in electrical conductivity of the template molecule and a change in the energy required to dissociate the target molecule and the template molecule. The magnitude of the change is indicative of the specific identity of the target molecule.

FIELD OF THE INVENTION

This document pertains generally to sensor devices, and moreparticularly, but not by way of limitation, to detection and analysis ofa target substance.

BACKGROUND OF THE INVENTION

Previous efforts to detect analytes, such as biological agents,pathogens, bacteria, viruses, fungi, molecules and toxins are relativelycumbersome, time-consuming, and require significant technical expertiseto operate. For example, one technique generally requires the incubationof samples on Petri plates over an extended period of several days.Another technique involves the use of dyed antibodies selected toidentify the presence of specific pathogenic bacteria.

In addition, some systems require that the target biological moleculesundergo an amplification procedure which is prone to errors and requiresa high level of technical skill. Furthermore, amplification sometimescannot determine the concentration of a target biological agent and arenot practical for use in the field.

Some systems fail to detect natural or engineered changes in biologicalagents, are known to generate false positive errors and are sensitive totesting conditions. Some devices for the detection of biologicalmolecules (such as DNA sequences or proteins) require a large number oftarget molecules to operate effectively. Accordingly, the targetmolecules must be amplified, and in some instances tagged which preventsfurther use of the template molecules.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsdescribe substantially similar components throughout the several views.Like numerals having different letter suffixes represent differentinstances of substantially similar components. The drawings illustrategenerally, by way of example, but not by way of limitation, variousembodiments discussed in the present document.

FIG. 1 illustrates a flow chart for a method of detecting a targetmolecule.

FIG. 2 illustrates a cantilever detector.

FIG. 3 illustrates a portion of a cantilever structure.

FIG. 4 illustrates a graph of displacement as a function of time.

FIGS. 5A and 5B illustrate a cantilever detector system.

FIG. 6 illustrates a graph of current as a function of voltage.

FIGS. 7A and 7B illustrate measured parameters as a function of time.

FIG. 8 illustrates a shift in resonance.

FIG. 9 illustrates a flow chart for a method of preparing a templatemolecule.

FIGS. 10 and 11 illustrate flow charts for methods of detecting a targetmolecule.

FIG. 12 schematically illustrates an array of cantilevers in a system.

FIG. 13 illustrates an example of a portable detector.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description includes references to theaccompanying drawings, which form a part of the detailed description.The drawings show, by way of illustration, specific embodiments in whichthe invention may be practiced. These embodiments, which are alsoreferred to herein as “examples,” are described in enough detail toenable those skilled in the art to practice the invention. Theembodiments may be combined, other embodiments may be utilized, orstructural, logical and electrical changes may be made without departingfrom the scope of the present invention. The following detaileddescription is, therefore, not to be taken in a limiting sense, and thescope of the present invention is defined by the appended claims andtheir equivalents.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one. In this document, the term“or” is used to refer to a nonexclusive or, unless otherwise indicated.Furthermore, all publications, patents, and patent documents referred toin this document are incorporated by reference herein in their entirety,as though individually incorporated by reference. In the event ofinconsistent usages between this document and those documents soincorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

The accompanying drawings that form a part hereof, show by way ofillustration, and not of limitation, specific embodiments in which thesubject matter may be practiced. The embodiments illustrated aredescribed in sufficient detail to enable those skilled in the art topractice the teachings disclosed herein. Other embodiments may beutilized and derived therefrom, such that structural and logicalsubstitutions and changes may be made without departing from the scopeof this disclosure. The detailed description, therefore, is not to betaken in a limiting sense, and the scope of various embodiments isdefined only by the appended claims, along with the full range ofequivalents to which such claims are entitled.Such embodiments of the inventive subject matter may be referred toherein, individually or collectively, by the term “invention” merely forconvenience and without intending to voluntarily limit the scope of thisapplication to any single invention or inventive concept if more thanone is in fact disclosed. Thus, although specific embodiments have beenillustrated and described herein, it should be appreciated that anyarrangement calculated to achieve the same purpose may be substitutedfor the specific embodiments shown. This document is intended to coverany and all adaptations, or variations, or combinations of variousembodiments. Combinations of the above embodiments, and otherembodiments not specifically described herein, will be apparent to thoseof skill in the art upon reviewing the above description.

Introduction

Molecules are affected by changes in their environment. For example, asingle stranded deoxyribonucleic acid (ssDNA) will respond to theintroduction of its complementary ssDNA. Hybridization of one DNA strandwith its complementary strand results in a reduction in overall length,as well as a change in DNA conductive properties. The changes aredirectly proportional to the fidelity of match between the two DNAstrands with even a single nucleotide mismatch having a measurableeffect. Analysis of the changes permits identification of variouspathogens and allows differentiating between specific strains.

In one example, a microelectromechanical (MEMS) structure is used tomeasure molecular changes associated with hybridization. For example, amobile element in a MEMS chip is bridged by a selected single-strand DNAfragment. A complementary fragment is detected and identified based on ameasurement of the deflection of the element and a measurement ofconductivity resulting from hybridization. In one example, signalprocessing is used to interpret the hybridization events as detectionand identification. The correlation of length and conductivity change toDNA strand homology is used to discriminate between known and variantpathogens, and between benign and virulent strains.

In addition, a voltage applied after hybridization causes the pathogenDNA strand, or target molecule, to be released from the templatemolecule. The current at which the target molecule releases can alsoprovide information to identify the target molecule. In addition, byreleasing the target molecule, the sensor can be prepared for anadditional detection event. Furthermore, the integrity of the sensor istested by conducting a low-level current through the template moleculeprior to a sensing event to verify continuity. In one example, an arrayof DNA-bridged MEMS sensors allows simultaneous multiplexed detection ofnumerous viral or bacterial pathogens, or enables the measurement ofconcentration of a single pathogen.

In addition, changes in the resonance of the template molecule are usedfor identifying a sample that binds to the template molecule. In oneexample, a movable end of a cantilever is bridged to a structure by atemplate molecule. The resonance frequency of the cantilever system(with the template molecule bridge) will change upon hybridization ofthe sample with the template molecule. The degree of homology can bedetermined by the magnitude and direction of the shift in amplitude orfrequency.

Exemplary Method

FIG. 1 illustrates exemplary procedure 100 for detecting and identifyinga target substance. The target substance, in one example, includes asingle strand DNA fragment.

As used herein, the target molecule and the template molecule are coinedterms and the molecules are related in the manner of their bindingtogether. Accordingly, a particular sensor uses a first ssDNA strand asa template molecule and a second ssDNA strand is a target molecule,another sensor can use the first ssDNA strand as the target molecule andthe second ssDNA strand as the template molecule.

Other combinations of binding partners are also contemplated. Forexample, either the template molecule or the target molecule can includenucleic acid molecules (e.g. oligonucleotides, including ss-DNA or RNAreferred to as ss-RNA), proteins and carbohydrates. A template moleculecomprising a single strand of DNA may hybridize with a complementarystrand of DNA to form a double stranded DNA (ds-DNA). In addition, atemplate molecule including a protein may bind to a target molecule thatalso includes a protein (through a protein-protein recognition), anucleic acid (through protein-nucleic acid recognition) or acarbohydrate (through protein-carbohydrate recognition). In addition, atemplate molecule including nucleic acid may bind to a target moleculeincluding a nucleic acid using DNA (through nucleic acid-nucleic acidrecognition) or a carbohydrate (through nucleic acid-carbohydraterecognition). Furthermore, a template molecule including a carbohydratemay bind to a target molecule including a carbohydrate (throughcarbohydrate-carbohydrate recognition). In general, templatemolecule-target molecule combinations can be described as a lock-and-keymechanism that allows certain molecules to bind only with othermolecules.

At 105, the sample to be analyzed is collected. The sample, whichpotentially includes the target molecule, can be in a gas, liquid orsolid form. At 110, the sample is prepared for analysis, which, in oneexample, includes filtering of the sample. At 115, the sample isdelivered to the sensor for analysis. Sample delivery, in one example,includes routing the sample using a microfluidic pump, valve, channel,reservoir or other structure. At 120, the sample is introduced to one ormore sensors for possible detection and identification. In variousexamples, detection and identification include monitoring for a changein length or position, a change in a force, a change in electricalconductivity or resistivity, determining a signal level for disbonding asample from the template molecule and determining a shift in resonance.At 125, the collected data is processed to detect and identify thesample. Processing the data, in various examples, includes comparing anoutput signal with stored data where the stored data includes a look-uptable which correlates a target molecule with a template molecule.

Other procedures are also contemplated. For example, a sensor integritytest may be performed before exposing the sensor to the sample bymonitoring various parameters.

Exemplary Cantilever Sensor

FIG. 2 illustrates sensor 200 according to one example. Substrate 215provides a structure or reference stage upon which the cantilever isfabricated. Base 210 is affixed to one end of cantilever 205A andelevates cantilever 205A above substrate 215. In one example, cantilever205A has dimensions of approximately 200 μm in length by 20 μm in widthand 1 μm in thickness. A portion of template molecule 220 is affixed toa free end of cantilever 205A.

The figure illustrates template molecule 220 as a linear element havingone end bonded to the free end of cantilever 205A and another end bondedto a portion of substrate 215. The space between cantilever 205A andsubstrate 215 is bridged by template molecule 220.

In the figure, template molecule 220 is shown at a time where nocomplementary binding partner has bonded and cantilever 205A is shown ina relaxed or unloaded state. Alternative positions for cantilever 205Aare illustrated in dotted lines. Cantilever 205B, for example, isillustrated at a time when a binding partner has associated withtemplate 220. Cantilever 205B has been displaced by distance D1 belowthe position shown by cantilever 205A. Template molecule 220 isassociated with a binding partner of low affinity. Cantilever 205Cillustrates a time when a different binding partner has associated withtemplate 220. Cantilever 205C has been displaced by distance D2 belowthe position shown by cantilever 205A. Cantilever 205C represents thecase when template molecule 220 is associated with a binding partnerwith greater affinity than the binding partner represented withcantilever 220B.

Displacement of cantilever 205A is detected, in one example by anoptical detection system. In the figure, optical source 230 projectslight beam 250 on a surface of cantilever 205A which is reflected, asshown by ray 245A, and detected by cell 240A of optical sensor 235.Cantilever 205B reflects light, as shown by ray 245B which is detectedby cell 240B and cantilever 205C reflects light, as shown by ray 245Cwhich is detected by cell 240C. Sensor 235 is illustrated as havingthree cells, however, more or less are also contemplated. In oneexample, optical source 230 includes a laser or other source ofcollimated light.

Other means for detecting displacement or resonance of cantilever 205Aare also contemplated. In one example, a piezoelectric element providesan electrical signal as a function of deflection of cantilever 205A. Thepiezoelectric element includes a piezoelectric material that is bondedto, or integrated with, a surface of cantilever 205A, base 210, or otherstructure.

In one example, a measure of capacitance is used to determinedisplacement or resonance. For example, a conductive layer of acantilever structure serves as a capacitor plate. Capacitance betweenthe conductive layer of the cantilever and another conductor varies withthe distance between the conductors. Thus, a measure of capacitance canprovide displacement and resonance data. In various examples, theconductive layer of the cantilever is electrically isolated from otherconductive layers of the cantilever.

In one example, a magnetic or electric field is used to determine thedisplacement or resonance of a cantilever structure. Relative motionbetween a magnet and a conductor provides a signal used to determinedisplacement or resonance. In addition, a strain gauge affixed to acantilever provides displacement and resonance information.

Exemplary Cantilever Structure

FIG. 3 illustrates an example of a sensor structure fabricated usingDirected Template Circuitry (DiTC) construction. Directed templatecircuitry uses microelectromechanical systems, self assembled monolayers(SAMs), and DNA hybridization. Using lithography, thin films of variousmaterials, including metals such as silver (Ag), chromium (Cr), gold(Au) and carbon, are patterned in micron size dimensions. Self assembledmonolayers allow selectively immobilizing template molecules on a MEMSsurface. In addition, proteins and other biomolecules can be immobilizedonto surfaces such as gold using SAMs. Moreover, target analytes can bedetected using amperometric methods and SAMs on electrodes.

In one embodiment of the directed template circuit, SAMs technology isused to apply a monolayer of the protein streptavidin on gold which islayered on chromium. Streptavidin is immobilized on the gold electrodesurface based upon binding the protein to a biotinylated disuldemonolayer on the gold surface.

The same biotin based chemistry is then used to bind betweenapproximately 20 and 100 base oligonucleotides primers specificallydesigned and synthesized to hybridize to the single-stranded DNAtemplate bridge as shown in FIG. 8. The directed template circuitryprimers direct the orientation and positioning of the ssDNA templatebridge, i.e. the left-hand primer.

In one example, a single-strand DNA (ssDNA) template is bound usingoligonucleotides primers in a manner that bridges an electronic MEMSbased circuit. Hybridization to target DNA derived from themicroorganism being identified causes a reduction in distance betweencantilever arms.

Manufacturing of MEMS microchip devices using directed templatecircuitry entails, briefly, a gel photopolymerization technique toproduce micromatrices of polyacrylamide gel pads separated by ahydrophobic glass surface. In one example, DNA oligonucleotides areapplied to the gel pads and tested for proper positioning andorientation by fluorescence microscopy and exonuclease digestion.

Other methods can be used to attach the template molecule to the contactpoints in a manner that aligns the template molecule for detection andidentification of a target molecule. For example, bonds establishedusing gold-Streptavidin and sulfur group/biotin are also contemplated.

In one example, the primers are designed and synthesized to hybridize toa template molecule comprising a single stranded DNA molecule.Furthermore, the primers are arranged and oriented so that the templatemolecule will have a desired orientation and position. Moreparticularly, the primers ensure that a selected portion (at or towardsa first end) of the template molecule is bound to one surface of thecantilever and that a selected portion (at or towards a second end) ofthe template molecule is bound to another surface of the cantilever. Invarious examples, the ends of the template molecule are keyed to aspecific portion of the cantilever structure (one way alignment) or notkeyed (two way alignment)

Performance—Displacement

In one example, the strength of a DNA strand, and the length, isdependent upon base composition, sequence and the environment. Ameasurable biophysical phenomenon occurs when a single strand of DNAinteracts with its complementary strand. In particular, the average freereduction in DNA length upon hybridization with its complements isapproximately 40%. DNA nucleotide sequence and composition can becorrelated with structural and other biophysical parameters.

FIG. 4 illustrates a relationship between force amplitude anddisplacement of a surface of cantilever 205A. For a particularcantilever, the measured performance can be used to identify acomplementary binding partner. If a cantilever is exposed to a samplemolecule that is not a completely complementary, then results will bedifferent.

FIG. 4 graphically illustrates the strength of a biological molecule forone example. For the data presented, a molecule is tethered between thecantilever tip and a substrate. The tethering is accomplished by addinga functional group to the ends of the template ssDNA for attachment tothe cantilever on one end of the sequence and to the substrate at theother end. Exemplary combinations include gold-Thiol bonds andbiotin-streptavidin bonds.

Analysis of data to establish the molecular tensile strength ispresented in the figure. In one example, the sensor structure isfabricated such that the template molecule is held in slight tension,however, a neutral or near zero tension is also contemplated. With thetemplate molecule held in such a manner, a binding partner isintroduced. For a template molecule of ssDNA, a suitable binding partneris the complementary ssDNA strand. The subsequent binding (orhybridization) of the template molecule with the target moleculeprovides a measurable change in a physical parameter or characteristic.The cantilever is able to detect (and measure) displacement and thechange in length of the molecule due to hybridization.

The figure illustrates cantilever displacement relative to hybridizationof a template ssDNA with a target ssDNA. As noted, the cantileverdeformed by approximately 10.2 nm after exposing the template ssDNA witha genetically matching (or complementary) target ssDNA. Thisexperimental approach was repeated on more than 100 different biologicalmolecules.

In the figure, standard target represents a complementary ssDNA strandwith 100% homology with the template molecule (strand). Other targetsare illustrated at 2%, 19% and 38% variant from the 100% homologouscomplementary ssDNA strand. As used herein, the term variant denotes atarget ssDNA containing random base pair substitutions relative to the100% homologous complementary ssDNA strand. The gradations noted in thefigure illustrate that variant ssDNA molecules are also detectable andidentifiable using the present system.

Exemplary Dual Cantilever Detector

FIGS. 5A and 5B illustrate views of cantilever based sensor 500. FIG. 5Aillustrates template molecule 545 bridging, or linking, the free ends ofdual cantilevers 505A. Cantilevers 505A are electrically coupled todetector circuit 530 via conductors 550 and connection plates 535disposed at stabilized ends of cantilevers 505A. Connection plates 535are bonded to layer 510 which is disposed atop layers 515 and layer 520.Layers 510, 515 and 520, in one example, are comprised of Si3N4, Si,Si3N4 each having a thickness of approximately 50 nm, 150 nm and 250 nm,respectively. Cantilevers 505A are suspended above sample channel 540formed in layer 515. Cantilevers 505A, in one example, are formed oflayer 555 (gold) and layer 560 (chromium) having thicknesses ofapproximately 40 nm and 5 nm, respectively.

In FIG. 5A, cantilevers 505A are bridged by a template molecule of ssDNA545 under little or no tensile forces. Detector circuit 530, in oneexample, provides an electrical current to detect the level ofconductivity. It will be appreciated that conductivity is the reciprocalof resistance and in one example, a resistance is determined. In oneexample, an impedance value is determined. In FIG. 5B, bridge 565represents a hybridized dsDNA formed by the combination of the templatemolecule (ssDNA) and the target molecule (ssDNA). As illustrated in FIG.5B, cantilevers 505A are convergently deflected. Detector circuit 530generates a measurement of conductivity and upon hybridization of thedsDNA strand, reflects a measured increase in conductivity.

In various examples, a test circuit and a reset circuit are provided indetector circuit 530. The test circuit is configured to provide acurrent to template molecule 545 to establish that the template moleculeis properly affixed to the cantilever arms. For example, a seriescombination of a current source, sensor and a resistor will indicate anexpected current flow if the sensor and template molecule are properlyconfigured. Deviations from an expected current level may indicate thatthe template molecule or the sensor is not properly configured forsample testing.

A reset circuit of the detector circuit includes a driving circuit fordisbonding the target molecule from the template molecule in preparationfor another detection and identification event. In one example, thisentails providing a ramping voltage to the template molecule andmonitoring for a peak current. In one example, this entails providing aramping current to the template molecule and monitoring for a peakvoltage. The peak voltage, or current, will coincide with a denaturingor disassociating event of the template molecule and the targetmolecule.

FIG. 6 illustrates an example of current required to induce denaturationof tethered DNA from a complementary strand. The reset circuit, or othermeans of providing a denaturation current can remove the complementarystrand from a sensor site, thereby readying it for a new sensing event.In one example, a sensor disposed in a flow stream can be used forsuccessive and separate sensing events, thus, enabling continuousoperation of the sensor.

In the figure, denatration current is indicated on the ordinate andapplied voltage appears on the abscissa. The difference in currentmagnitude, as illustrated, provides a means for discerning variationsfrom a complementary target molecule.

A high degree of proportionality is noted between the amount of currentrequired to force denaturation and the degree of mismatch of thetemplate and target ssDNA strands regardless of whether the variationoccurred on one region of the genetic sequence or was spread out over anumber of different locations along the sequence of the target.

FIGS. 7A and 7B illustrate a manual process of increasing the voltage toforce denaturation followed by a reduction in the voltage back tosensing levels to allow another hybridization to occur. As illustratedin FIG. 7A, a number of sensing events are noted. Reset signals areillustrated in FIG. 7B, as corresponding to those sensing events. Adenaturation current provides a means of resetting the sensor. Thedenaturation current appears consistent, both during the ssDNA and afterhybridization (dsDNA) states.

In the figure, a complementary strand was introduced at approximately 15seconds from the start of the data acquisition followed by an immediatesensing event. After several seconds, the voltage was manually increasedto approximately 4 volts, resulting in denaturation of the doublestranded DNA. The voltage was manually reduced to 3 volts, and thesystem was thus reset for another sensing event.

Resonance Example

FIG. 8 includes graphical data 800 illustrating how resonance can beused to identify and detect a target molecule using a bridged templatemolecule.

In the figure, frequency is plotted on the abscissa and amplitude on theordinate. The cantilever structure, or other suspended structure isdriven to oscillate using an excitation signal. In various examples, theexcitation signal is provided by a magnetic, piezoelectric or acousticalmember disposed near the movable structure. In the figure, curve 805illustrates an example wherein the template molecule resonates at aninitial frequency of F₂ and with an initial amplitude of A₂. Afterexposing the template molecule to the target molecule, the structureresonates with a frequency of F₁ and with an amplitude of A₁. Frequencydifference Δ_(F) and amplitude difference Δ_(A) are indicative of thedegree of homology and therefore, allow detection and identification ofthe target molecule. For example, it is believed that a target moleculewith a higher percentage of match with the template molecule willexhibit a greater change in either or both of the amplitude and thefrequency.

The figure illustrates a reduction in both the amplitude and thefrequency. However, in other examples, either or both of the amplitudeand frequency may exhibit an increase or a decrease.

In one example, resonance of the mobile portion of the MEMS deviceallows detection and identification. In one example, an end of thecantilever includes a magnetic material and an alternating currentpassed through a coil disposed under the cantilever causes thecantilever to vibrate at the frequency of the alternating current. Inone example, the dimensions of the cantilever and the alternatingcurrent are selected to maximize the output. For example, if thealternating current is near the natural frequency of the cantilever, theresponse of the structural system will be maximized. The stiffness ofthe structural system is changed when the ssDNA, or other templatemolecule, is tethered between the end of the cantilever and thesubstrate base. Either or both the amplitude of the displacement of theoscillating system and the oscillation frequency will differ from thatof the system with the free cantilever end. Upon introduction of atarget molecule (such as an analyte or the ssDNA complement to thetemplate ssDNA), the amplitude of the displacement and frequency of theoscillating system will change. The amount of the change will beproportional to the degree of homology between the template and targetmolecules since the stiffness of a dsDNA strand is greater than the sumof the stiffnesses of two independent ssDNA. Thus, in addition to thedetection of the presence of the analyte, the change in amplitude andfrequency can be used to measure the degree of homology of the ssDNAmolecules when compared to that of a complementary match.

Exemplary Preparation

FIG. 9 illustrates a flow chart of method 900 according to one example.In the figure, a cantilever is formed on a base at 905. Structures otherthan a cantilever are also contemplated, including, for example, acircular or helical structure having one supported end and a free end.In addition, a disc-shaped or rectangular structure is also contemplatedwith a movable center region and a perimeter affixed to a base structurein the manner of a drum head. In one example, semiconductor fabricationtechniques are used for the formation of the cantilever on the base.

At 910, a bonding material, or primer, is applied to the cantilever andto the base structure or substrate. The primer is selected to assurethat the template molecule is affixed with proper alignment andorientation. In various examples, the primer includes gold andstreptavidin.

At 915, the template molecule is bridged between the substrate and thecantilever.

In one example, method 900 is performed by a manufacturer in preparing asensor for a particular application.

Exemplary Detection and Identification

FIGS. 10 and 11 illustrate testing methods 1000 and method 1100,respectively. The methods illustrated, as well as other methods, can beimplemented using a computer, or other control circuitry, coupled to asensor. In one example, the method is executed using manual control ofthe sensor.

In FIG. 10, the sample is prepared at 1005. Sample preparation, invarious examples, entails filtration, purification, amplification andother procedures to ready the sample for analysis.

At 1010, the template molecule is analyzed to establish one or moreparameters to serve as a baseline. In one example, this entailsverifying that the template molecule is properly aligned and positionedby verifying a current level through the template molecule. In addition,the conductivity or resistivity, resonant amplitude and frequency forthe template molecule alone is measured. In one example, the physicalposition of the template molecule is measured.

At 1015, the sample is exposed to the template. In one example, thisentails injecting a sample, which possibly includes the target molecule,into a channel or reservoir of the test apparatus. The channel orreservoir is in communication with the template molecule.

At 1020, the template molecule is analyzed to generate a physicalparameter corresponding to the exposed template molecule. The exposedparameter, in various examples, includes measuring a change in aposition, or displacement, measuring a change in alignment, measuringconductivity or resistance, measuring a denaturing current and measuringchanges in resonance. Other physical parameters are also contemplated,including those based on a color or optical property of the combinationof the template and target molecules.

At 1025, a query is presented to determine if a difference is notedbetween the baseline and the parameter after exposure of the sensor tothe target molecule. If a change in the physical parameter, or adifference, is noted, then processing continues at 1030 where the sampleis identified. The existence of a difference is indicative of detectionof the template molecule.

As noted elsewhere in this document, the degree of homology isindicative of the match between the template molecule and the targetmolecule. Other binding pairs are also contemplated and proximity to acomplete match can be correlated to the difference noted in the physicalparameters.

In one example, a memory coupled to a processor of the present subjectmatter includes stored data in the form of a look-up table. The storeddata provides a correlation between the differences or changes noted ina physical parameter and the degree of homology.

If the query at 1025 yields a negative answer, then processing continuesto 1035 where an output signal is generated. The output signal, invarious embodiments, includes a measure of the difference or changenoted, the degree of homology or the identification of the targetmolecule.

At 1040, the template molecule is cleared of any remaining targetmolecule or sample material, or reset, by applying an electricalexcitation to the template molecule and inducing denaturation ordisbonding.

In one example, following 1040, the method returns to 1005 for detectionand identification of an additional sample.

FIG. 11 illustrates method 1100 which includes a serial testing of asample. It will be appreciated that other orders of testing are alsocontemplated as well as parallel testing. For example, measurement of achange in resonant frequency, resonant amplitude and conductivity can beperformed concurrently. In method 1100, the initial conditions, orbaseline, established at 1105.

At 1110, the displacement of the sensor, due to the template moleculehybridizing with the target molecule, is determined. At 1115, a shift inresonance is determined. The shift may correspond to a change in theresonant frequency or the resonant amplitude. At 1120, the conductivityof the template molecule with target molecule is determined. At 1125, adisbonding current, or heat level, is determined by monitoring for apeak signal.

FIG. 12 illustrates an array of cantilever sensors fabricated onsubstrate 1205 having common base 1210. The cantilevers, some of whichare labeled 1240A, 1240B, 1240C and 1240D are affixed to base 1210 onone end and tethered by template molecules to contact points 1245A,1245B, 1245C and 1245D, respectively, on a surface of substrate 1205.The template molecules, in one example, are of identical composition andprovide a level of redundancy for testing. In one example, at least twotemplate molecules are different and are tailored to detect and identifydifferent target molecules.

Each cantilever, such as 1240A, is coupled to controller 1215 byelectrical conductors 1235A and 1235B using multiplexer 1220. Controller1215 selectively applies testing current, voltage, drive signals orother signals to enable each cantilever to detect and identify a targetmolecule. Power source 1225, of controller 1215 provides a constant orramped voltage or current for excitation. In one example, power source1225 provides a denaturing current or voltage. In one example, powersource 1225 provides a drive signal to excite resonance in eachcantilever.

Interface 1230 is coupled to controller 1215 and provides data entry anddata output. In various examples, interface 1230 includes a display, atouch sensitive screen, a keyboard, a keypad, a mouse or other pointercontrol, an audio transducer, a storage device, a printer, a networkconnection (for example, a wide area network such as the Internet, or alocal area network such as an intranet), an electrical connector or awireless transceiver.

FIG. 13 illustrates exemplary portable device 1300 according to oneembodiment. In the figure, display 1305 provides visual prompts and datacorresponding to analysis of a target molecule and device condition.User accessible controls and data entry points include power button1310, reagent cut 1315, sample input 1320 and controls 1325. Othercontrols and data entry devices are also contemplated. In one example, apermeable surface on device 1300 allows a user to deliver a sample usinga syringe or other injection device. In one example, a port on a surfaceof 1300 includes a reservoir to receive a sample.

Device 1300 is illustrated as a portable, battery operated device,however, other embodiments are also contemplated, including for example,a desk-top unit with accommodations for receiving a sample and providingan output.

Example

In addition to measurable changes in length or force, the capacity ofDNA structures to conduct an electrical current is related to content,sequence, length, and bridged circuit chemical environment. In oneexample, conductivity is related to levels of guanine/cytosine.

In one example, a 121 base pair (bp) Bacillus genomic DNA sequence wasisolated from genomic, plasmid, and lambda viral DNA. Data indicatesconsistent results using numerous variables with regard to DNAproperties (length, sequence composition) and analysis conditions(redox, pH, salt, denaturant, and hybridization accelerant controls) andother DNA (single and double stranded), molecules and genetic variantsisolated from Bacillus as well as E. coli DNA.

The subject fragment was isolated from Bacillus genomic DNA byrestriction endonuclease digest and ligated into a pUC 13 plasmidcloning vector that was transformed into an E. coli host as the parentalstrain. A library of random genetic point mutations were created alongthe length of the plasmid insert and isolates with inserts that variedfrom the parental by 2%, 19%, and 35% were sequenced and used forfurther analysis. Both parental and variant inserts were excised fromthe host plasmid and the 5′ and 3′ ends were chemically modified with athiol and biotin groups. Single strand DNA was isolated using affinitychromatography (based upon the biotin modifications) and attachedbetween streptavidin and gold coated conductive atomic force microscopy(AFM) tips and stages. The AFM tip is initially undeflected. In oneexample, the change in effective length of a single strand of DNA as ithybridizes to its complementary strand is a reduction of 40%.

AFM tip displacement was observed within seconds of introducing the DNAcomplement (in hybridization solution) or genetic variants to thetethered DNA template. The experimental results indicated a consistenttip displacement (<0.5% COV) as a function of the degree of mismatchbetween template and complement. It is postulated that base-pairmismatches did not contribute to overall structure helical formation,thus reducing the reduction of molecule length.

Electrical conductivity was determined utilizing conductive AFM tips.The same 121 bp fragment was tethered between AFM tip and stage and theDNA complement was introduced. Electrical current (in nanoamps) wasmeasured as a function of time at a fixed voltage.

Prior to the introduction of the complementary DNA, the applied voltageresulted in a consistent, or baseline, current (of approximately 0.3 nA)passing through the tethered ssDNA. Treatment of the tethered ssDNA withDNA nuclease resulted in a loss of this baseline current. Heat treatednuclease did not result in a loss of current.

Measurable current through a sensor provides a verification of sensorfunction (sensor self-test) since electric current will flow if thessDNA remains tethered to the MEMS mobile elements. Followinghybridization between the tethered ssDNA and its complementary strand,an increase in current appears as noted in the figures. In addition, thefigures illustrate a relationship between measured current and thedegree of match between the strands. After hybridization, the conductedcurrent remains relatively consistent as long as the voltage is appliedto the sensor site.

After hybridization, the applied voltage was increased and the conductedcurrent correspondingly increased to a peak level. Denaturation of thetethered ssDNA and the complementary strand occurred at a potential ofapproximately 4.1 volts for this particular 121 bp fragment. The amountof current associated with denaturation varied with the degree of matchbetween the tethered ssDNA and the complementary strand. Concurrent withthe drop in current, the AFM tip returned to an undeflected position. Itis postulated that the higher level of current infuses sufficient energyinto the hybridized strands such that they can no longer remainhybridized although other mechanisms or factors may be responsible forthis phenomena. The base pair mismatches present in the variants appearto introduce insulating locations along the strands, therebyproportionately reducing conductance.

In one example, the selection of a template molecule, such as particularDNA, to bridge a circuit or cantilever structure affects DNAspecificity, length, sequence, composition and conductivity. In oneexample, detection and identification specificity is enhanced byselecting ssDNA from multiple genetic regions of a pathogen fortethering. In one example, a longer DNA segment provides increasedspecificity (DNA sequence that is unique to the specific biologicalagent target). In one example, a shorter DNA segment allows selection ofregions of high guanine (G) and cytosine (C) content. GC overallcomposition and sequence provides insulating characteristics of adenine(A) and thymine (T). High AT content in DNA leads to inflexibility andoverall molecular curvature depending upon the relative positioning ofAT-rich regions (i.e. in phase with the helical rotation). In variousembodiments, selected DNA segments were greater than 40% GC, or greaterthan 60% GC. DNA segment length was therefore less than 500 base-pair(bp), or less than 150-200 base pair (bp). Determination of DNA GCcomposition, sequence, and specificity was determined using commerciallyand publicly available software such as PubMed BLAST(www.ncbi.nlm.nih.gov/). Other software is available to correlate firstorder molecular parameters to higher order features (i.e. flexibility,curvature). In one example, the template molecule is selected using asoftware algorithm.

ADDITIONAL EXAMPLES

In one example, the sensor includes a suspended member which includes acantilever. The template molecule is affixed to a contact point, atleast one of which is located on the suspended member. The cantilever,in various examples, is curved, circular or web shaped. In one example,the suspended member is a rotary member that turns about an axis. As arotary member, the contact point is displaced along an arc when thetemplate molecule binds to the target molecule. In one example, one endof the rotary member rotates while another remains stationary or rotatesin an opposite direction or through a smaller range and the phasedifference between the two ends of the rotary member provides adifference signal that is used to discern the target molecule.

In one example, the template molecule has more than one binding sitespecific to a target molecule. In one example, the target molecule hasmultiple binding sites, each of which is specific to a different targetmolecule. In one example, the target molecule has multiple bindingsites, each of which is specific to a single target molecule.

In one example, multiple contact points are provided on a sensor and thetemplate molecule binds to two or more of multiple contact points. Forexample, a double-ended template molecule can bind to a sensor havingtwo, three or more contact points. As another example, a three-endedtemplate molecule can bind to a sensor having two, three, four or morecontact points.

In one example, an output signal is generated as a function of a changein a measure of a physical parameter. Physical parameters includestructural as well as electrical parameters. Exemplary structuralparameters include positional changes such as physical displacement,resonant frequency, resonant amplitude, physical alignment ororientation of a contact point and a reference point, a force exerted onan axis, heat generated and optical changes including color. Otherphysical parameters are also contemplated.

In one example, an output signal is generated as a function of a changein a measure of an electrical parameter. Exemplary electrical parametersinclude impedance, conductivity, resistivity, inductance, capacitance.In addition, an electrical parameter can be described as an outputsignal in the presence of an input signal. For example, a change incurrent conducted in a template molecule can result in a change involtage. In addition, a change in voltage applied to the templatemolecule can result in a change in a current. Other driving signals canalso be applied and measured responses can be used to generate an outputsignal. Other electrical parameters are also contemplated.

In one example, a physical parameter includes a measurement ofelectrical conductivity. Electrical conductivity is a measure of theflow of electrons in a material. Electrical conductivity is thereciprocal of resistivity, or resistance, and in one example, themonitored physical parameter includes resistivity.

In one example, a ssDNA template molecule, bound via oligonucleotidesprimers, bridges an electronic MEMS based circuit. Hybridization to atarget molecule (such as DNA) is derived from the microorganism beingidentified and causes a reduction in the distance between the cantileverelements.

In various embodiments, a comparator or Wheatstone bridge is used todetect, identify and compare voltage levels, current levels,conductivity or other parameters.

In one example, denaturing of the template molecule is performed byapplying heat to the template and target molecules. A level of heat isquantified by measuring a current, voltage or wattage. In one example, adifference in the level of heat is correlated to the identity of thetarget molecule.

In one example, a single sensor site includes a tethered, single strandDNA (ssDNA) bridging a mobile element on a micro electromechanicalsystem (MEMS) chip. In one example, hundreds or thousands of such sitesare placed on a single chip. The tethered ssDNA is selected to hybridizewith a complementary strand extracted from a bioagent of interest. Theresulting hybridization both changes the physical length of the tetheredmolecule, and changes the conductivity of the tethered molecule. Thechanges are measured in a MEMS system at a high signal-to-noise ratio.The degree of change is related to the degree of match between thetethered and bioagent DNA strands. Thus, the degree of variance(specificity) of the bioagent can be measured. After detection,identification and discrimination are confirmed, the bioagent DNA strandis expelled from the tethered strand by increasing the current flowthrough the molecule, thus resetting the sensor for subsequent sensingevents. Sensor viability is verified through a self-test since atethered ssDNA (absent its complement) is able to conduct a measurableamount of current.

The physical parameter changes are proportional to the fidelity of matchbetween the template molecule and the target molecule (or DNA strands) Asingle nucleotide mismatch yields a measurable change, thus enablingidentification of various pathogens and differentiation of subtlevariations between specific strains.

In one example, the template molecule includes ssDNA. In one example,specific DNA regions of B. anthracis are propagated and functionalized.The sensor can be bridged by DNA from any biological agent (bacteria,virus, or fungi).

In one example, four (4) 150-200 base pair (bp) segments of Bacillusanthracis (Ames) are selected for use as DNA bridge templates. In oneexample, for the purpose of testing the systems ability to discriminatebetween strains, alternative sequences to one of the templates wasdesigned. The variants differ from the parent molecule by randomnucleotide substitutions to generate 2%, 10%, and 20% variants. Templatemolecule selection is based upon calculated specificity, conductivityparameters, and flexibility. Species and strain specific segments werechosen from 16S rRNA fingerprint and virulence genes.

In one example, the four selected 150-200 bp templates and variants weresynthesized through commercially available DNA synthesis facilities. The150-200 bp DNA templates and variants were synthesized in ˜50 bp ssDNAfragments. Hybridization and ligation steps were used to create fulllength 150-200 bp templates. The templates were ligated into anappropriate plasmid cloning vector and a library of the DNA bridgetemplates were generated in preparation of large-scale plasmidproduction. Optionally, the selected 150-200 bp template candidates areexcised by restriction endonuclease digests or PCR amplified andsubcloned from Bacillus anthracis (Ames) DNA.

In one example, DNA bridge templates were covalently attached to AFM andMEMS surfaces via biotin-streptavidin and thiol-gold bonds. The plasmidborne templates were restriction endonuclease excised, and5-prime/3-prime biotin/thiol end-labeled with commercially availablekits. In one example, the templates were PCR amplified using biotin andthiol labeled primers.

In one example, DNA templates and variants were verified for sequenceintegrity through commercially available subcontracted DNA sequencingservices. The specificity of the each of the molecules was verifiedthrough standard Southern screening against genomic DNA of Bacillusanthracis strains (i.e. Ames, Sterne, A2012, 1055, Vollum, Kruger) andanthrax simulants (i.e. B. globigii, B. cereus, B. subtilis, B.thuringiensis) purchased commercially from the American Type CultureCollection or acquired through a material transfer agreement or othercollaborators.

In one example, atomic force microscopy (AFM) was used to measurespecific physical properties (i.e. displacement and conductivity) of theB. anthracis and variant ssDNA fragments. AFM tips and stages werecoated with gold and streptavidin and the thiol/Biotin end labeled DNAbridge templates were attached. AFM tip displacement and materialelectrical properties were measured prior to, during, and afterhybridization with complementary and variant ssDNA molecules and used asinput into MEMS device design. In one example, reagents to controlhybridization (pH buffers, salts), denaturation, hydrolysis andnucleotide oxidation were selected.

In one example, MEMS fabrication techniques are used for theconstruction of the sensor chips. In one example, fabrication entailsdeposition of thin films of material onto a substrate, application of apatterned mask onto the material using photolithographic methods andselective etching of the film using the resulting developed mask.Deposition of the material onto the substrate (silicon wafers) isaccomplished by chemical reaction-based approaches (chemical vapordeposition, epitaxy, electrodeposition, or thermal oxidation) or byphysical reaction-based approaches (evaporation, sputtering or casting).Removal of materials is accomplished through etching techniques. Thus,the circuitry for the device, using the application of patternedphotolithographic masks, is constructed using appropriate application ofinsulating and conducting material layers. The fabrication facilityincorporates the chip into packaging which, in one example, includes aceramic or plastic housing for the chip that includes the pinnedinterface for attachment to a printed circuit board (PCB).

In one example, upon fabrication of the MEMS chips, the DNA bridgetemplates are generated and tested. In one example, the MEMS mobileelements (cantilever end) includes thiol/gold and biotin/streptavidincovalent bonds. Single molecule attachment was accomplished byelectrostatic attraction. In one example, the device applies a 5 voltelectrical potential across the gap between the mobile MEMS elementswhere the tethered ssDNA is desired, in series with a 10 MΩ resistor.The ssDNA molecule is attracted to the resulting electrical field. Whenin close proximity, the biotin-streptavidin bonds on the substrate baseis formed, and the gold-thiol bonds is formed on the free end of thecantilever. When one molecule attaches in this manner, the potentialacross the gap is reduced due to the resistance in series in thecircuit. Thus, a single ssDNA molecule attaches at each site. Excess DNAthat does not bridge across the MEMS circuits is removed by DNAexonuclease digests. The circuit is stored in DNA stabilizing buffers(i.e., 300 mM NaCl, 10 mM Na citrate and 5 mM EDTA).

In one example, current measurement in the nano-amp range is performedusing integrated circuit amplifiers. A multiplexing integrated circuit(IC) amplifier and other electronics and processing are used to displaythe results of the sensing events. Analog signals taken from the MEMSchip are amplified and converted into digital signals.

In one example, a printed circuit board includes accommodations for theattachment of the MEMS chip and the IC chip. The board also includes adedicated main processing chip used to perform calculations and controlelectrical operations on the PCB. The PCB contains electrical interfacesfor the display and the battery, as well as the menu buttons. In oneexample, a program executed by the main processor uses the digitalsignals output from the IC to provide display. The user interfaceincludes controls to display and to set parameters that determine thedisplay characteristics, the threshold detection values, battery level,on/off and pathogen molecule purging control.

In one example, a plastic housing contains the printed circuit board(and attached bio- and IC-chips), sample flow paths, LCD display andcontrol buttons. In one example, an interior walls of the housingcontain ledges and slots to contain electronic components and precludeshifting inside the housing. In one example, the housing includes one ormore flow paths for introduction and removal of the reagents and sample.

In one example, electrical conduction through the sensor sites isgreater than 0.2 nA using AFM electronics. In one example, theintegrated circuit provides analog signal amplification >10 mVpeak-to-peak.

In one example, the sensor is configured to detect and identify preparedgenomic DNA of Bacillus anthracis strains and anthrax simulants (i.e. B.globigii, B. cereus, B. subtilis, B. thuringiensis), chemical and/ormechanically (sonicated) disrupted inactivated whole cell and spores ofthe previously mentioned anthrax strains and simulants, DNA and wholecells/spores in the presence of common contaminants and interferantssuch as postal dust, soil components, other chemical mixes, and mixedconsortia of microorganisms.

In one example, the system includes signal amplification, processing anddisplay sufficient to detect and identify a target molecule. In oneexample, electronic controls include on/off, mode, display control,battery life, self-test and reset functions. In one example, the systemincludes one or more flow passages to deliver a prepared sample to thesurface of a sensor configured to identify a single predeterminedpathogen, simulants or DNA target variants in a disruption solution.

In one example, the sample is collected outside of the system usingsurface wipe or batch air collector.

The present system includes a method and apparatus for determining thepresence, the identity or quantity of a target substance comprisingbiological or chemical analytes. In one example, an electronic circuitincluding at least one deflectable arm of a bio-electronic cantilever issurface treated to facilitate binding to a template polymer moleculethat undergoes a measurable change in a physical parameter in responseto environmental changes, such as the presence of a target moleculeassociated with a target substance to be detected. For example, a changein the physical configuration or dimensions of the template molecule istranslated into a deflection of a cantilever arm. In one example, achange in the electrical characteristics across the template molecule isdetected by hybridizing a single-stranded DNA bridge template to itscomplimentary strand. Such changes in physical properties or parametersare measured to provide information related to the presence and identityof a substance of interest. In one example, a number of such circuitsbridged by similar template molecules are provided and informationrelated to the concentration or quantity of the target substance can beobtained.

In one example, a microcircuit with geometry tailored for use within abiological agent detection device is provided for detecting the presenceof target and related biological agents or substances.

As used herein, a template molecule may be any molecule that will bind,or is likely to respond, to the presence or bind to a biological agentor a component of a biological agent. Accordingly, a template moleculemay comprise a naturally occurring or synthetically formed biologicalmolecule that will, or is capable of, selectively responding to, orbinding to, a target molecule associated with the target substance to bedetected. In one example, the template molecule includes an antibody,protein, nucleic acid, carbohydrate, glycoprotein or a polymer. In oneexample, the specific template molecule selected for detecting thepresence of a particular target molecule (or species or genus of targetmolecule) is selected such that the template molecule responds to, orbinds only with the exact target molecule or a related target molecule.In one example, a differential electric current or physical displacementresults from a biomolecule—biomolecule recognition between the templateand target. Accordingly, the relationship between a template moleculeand a target molecule may be that of complementary strands of nucleicacids, including ribonucleic acids (RNA) and deoxyribonucleic acids(DNA) and derivative molecules. Further examples of the relationshipbetween the template molecule and the target molecule include nucleicacid—nucleic acid recognition, protein—protein recognition,protein—nucleic acid recognition, protein—carbohydrate recognition,nucleic acid—carbohydrate recognition, and carbohydrate—carbohydraterecognition.

In one example, a biodetection device containing the described circuitincluding a template molecule spanning a gap between two surfaces, isprovided. In one example, the two surfaces are movable relative to oneanother. When the template molecule is exposed to, or bound to, a targetmolecule, the template molecule undergoes a dimensional change, alteringthe distance between the two surfaces. Accordingly, a biodetectiondevice in accordance with such an embodiment of the present inventioncan signal the presence of a target or related biological agent orsubstance when a change in the distance between the two surfaces isdetected.

In one example, the amount by which the distance between the surfaces isaltered is indicative of the molecule exposed to, or bound to, thetemplate molecule. For instance, a target molecule that is an exactmatch for the template molecule (i.e., an “exact target molecule”) mayresult in shortening the distance between the points of the templatemolecule interconnected to the two surfaces by an amount that is greaterthan the shortening that occurs when the template molecule is bound to amolecule that is related to but not an exact match for the templatemolecule. Accordingly, by measuring the amount by which the distancebetween the two surfaces has changed, information related to theidentity of the molecule bound to the template molecule is obtained.

In one example, a biodetection device containing the described circuitcapable of measuring the conductivity across a template molecule isprovided. In particular, a template molecule is interconnected to firstand second electrodes, such that it spans the gap between the twoelectrodes. When the template molecule is bound to a target molecule,the conductivity between the electrodes is altered. Accordingly, bydetecting a change in the conductivity between the electrodes, thepresence of a target molecule or related molecule can be detected.Furthermore, the amount by which the conductivity between the electrodeschanges is indicative of the molecule bound to the template molecule.For example, an exact target molecule will cause a greater change in theobserved conductivity between the electrodes than will a target moleculebound to the template molecule that is related but not identical to theexact target molecule.

In accordance with an embodiment of the present invention, a detectiondevice that can be reused, without requiring the replacement ofcomponents, is provided. In particular, by heating the templatemolecule, the target or related molecule can be unbound from thetemplate molecule. In accordance with an embodiment of the presentinvention, heating of the template molecule is accomplished by passing acurrent across the template molecule (and the bound molecule).Furthermore, the process of unbinding the target molecule from thetemplate molecule can be used to obtain information related to theidentity of the target molecule. In particular, the current appliedacross the template molecule (and target molecule) may be steadilyincreased or increased in steps, until a sudden change in theconductivity is observed, which indicates that the target molecule hasbeen dissociated from the template molecule. Because the current, andtherefore heat, necessary to unbind the target molecule is related tohow closely matched the target molecule is to the template molecule, theamount of current required to unbind the target molecule is anindication of the closeness of the match between the bound molecule andthe target molecule. For example, an exact target molecule would beexpected to require more energy to unbind it from the template moleculethan would a molecule that is not identical to the target molecule.

In one example, a biological agent detection device containing thedescribed circuit combining a number of detection mechanisms ortechniques is provided. For example, a detection device may determinethe presence of a target biological agent by detecting a dimensionalchange experienced by a template molecule, by detecting a change in theconductivity across a template molecule, or by determining the amount ofcurrent required to unbind a target molecule from the template molecule.Furthermore, information for identifying the target molecule may beprovided using such mechanisms or techniques.

In accordance with an embodiment of the present invention, a method fordetecting target substances or analytes by detecting a change in aphysical dimension associated with a template molecule is provided.According to such a method, a template molecule that undergoes a changein physical dimension when bound to a target molecule is exposed to asuspected biological agent or target substance (i.e., a substancesuspected of containing a target molecule). The suspected biologicalagent may be derived from a gaseous, liquid, or solid medium. If theexact target molecule or a related molecule binds to the templatemolecule, the resulting dimensional change in the template molecule isdetected, and the change reported. In accordance with a furtherembodiment, the method includes measuring the amount by which thephysical dimension of the template molecule has changed.

In one example, a method for detecting a target substance by sensing achange in the conductivity associated with the template molecule in thepresence of the analyte is provided. A template molecule capable ofselectively binding to an exact target molecule or related targetmolecule is exposed to a suspected biological agent. According to themethod, the conductivity across the template molecule is monitored. Uponbecoming bound to a target molecule, the resulting change in theconductivity across the template molecule is detected, and that changeis reported. In one example, the change in conductivity is measured.

In one example, a method for detecting the presence of a suspectedbiological agent by determining the amount of energy required to unbinda target molecule from a template molecule is provided. An electricalcurrent is passed across the template molecule—target molecule pair.Furthermore, the amplitude of the current may be increased, until asudden change in the conductivity across the template molecule isobserved, indicating that the target molecule has become unbound fromthe template molecule. Furthermore, the current at which the targetmolecule is unbound from the template molecule is used to characterizeor identify the target molecule that was bound to the template molecule.

The present system relates to the detection and identification ofbiological analytes. According to the present invention, targetbiological molecules are detected by sensing a change in a templatebiological molecule. The change in the template biological molecule mayinclude a change in a physical dimension of the template molecule, achange in the electrical conductivity observed across the templatemolecule, and/or the energy required to dissociate a target moleculefrom the template molecule. The magnitude of the change in a physicaldimension, change in conductivity, or amount of energy required todissociate a target molecule from a template molecule, may be measuredto determine the degree of homology between the target molecule and thetemplate molecule. In a further aspect, the present invention provides adetection method and apparatus that does not require the replacement ofcomponents in order to make multiple readings.

In one example, an electronic circuit is bridged by a template moleculeincluding a biological component or a representation of the biologicalcomponent. In one example, the circuit includes a MEMS-based structurebridged by a nucleic acid molecule, such as a DNA molecule, or amolecule that physically and chemically represents a single strand DNAmolecule. In one example, the MEMS circuit senses and responds to themotion and conductivity of a bridged DNA molecule as it hybridizes withits complimentary, or near complimentary DNA strand.

The following describes the selection and design of biologicalcomponents of the bio-electronic circuit.

As used herein, biological detection and identification devicespecificity refers to the ability of the system to specifically andaccurately identify a particular genus, species and strain of targetbiological agent. In the case of DNA-based biologicaldetectors/identifiers, the term specificity sometimes refers to theability of the DNA components of the system to specifically complimentand hybridize to DNA isolated from the biological agent. In order toenhance detection and identification specificity, here, multiple (in oneexample, more than three), biological agent DNA segments are selected.The DNA segment selection is based upon the calculated length,specificity, conductivity parameters and flexibility of the molecule tobridge the MEMS circuit. Longer DNA segments tend to retain greaterspecificity (DNA sequence that is unique to the specific biologicalagent target), and yet shorter DNA segments allow selection of regionsof high guanine (G) and cytosine (C) content. GC overall composition andsequence is related to the insulating characteristics of adenine (A) andthymine (T). In addition, high AT content in DNA leads to inflexibilityand overall molecular curvature, depending upon the relative positioningof AT-rich regions (i.e. in phase with the helical rotation). Thus,selected DNA segments may be greater than 40% GC, or greater than 60%GC. In one example, DNA segment length is less than 500 base-pair (bp),or less than 150-200 base pair (bp). Determination of DNA GCcomposition, sequence, flexibility, curvature, and specificity isdetermined through a number of privately, commercially, and publiclyavailable software such as PubMed BLAST (www.ncbi.nlm.nih.gov/). In oneexample, four DNA template segments are 100% homologous to Bacillusanthracis (Ames) and show lesser homology to other Bacillus species andstrains. Species and strain specific segments have been chosen from 16SrRNA fingerprint and virulence genes. In this embodiment, microorganismsoutside of the Bacillus genus fall below accurate detection andidentification thresholds. In one example, a matrix includes DNA-bridgedMEMS having DNA components that have specificity to other biologicalagents, and, in one example, is able to continuously monitor for thepresence of agents simultaneously.

The following describes the production of the biological components ofthe bio-electronic circuit.

In one example, specific DNA regions of the targeted biological agentare selected, generated, mass produced and chemically modified for thesake of adherence to a MEMS circuit. In addition, variants of the DNAregions are also generated and produced for the purpose of testing theproposed circuit for discrimination capabilities. In one example, avariant is a DNA molecule that differs from the selected DNA template innucleotide composition and sequence by 2% to 30%. In one example, fourselected 150-200 bp segments are either synthesized, PCR amplified, orsub-cloned from an actual targeted biological agent. High fidelity DNAsynthesis is generally limited to ˜50 bp ssDNA fragments that thenrequire hybridization and ligation steps in order to create the desiredfull length 150-200 bp DNA templates. The completed DNA templates arethen attached directly to MEMS lead surfaces if the 5-prime and 3-prime˜50 bp synthesized fragments were specifically labeled with attachmentligands. Alternatively the completed 150-200 bp templates are ligatedinto a plasmid cloning vector and a library of the DNA bridge templatesis generated in preparation for mass production. In one example, theselected DNA regions chosen to bridge the MEMS circuit leads may beexcised by restriction endonuclease digests or PCR amplified, andsub-cloned from the targeted biological agent.

The following describes verification of biological component integrity.

In one example, DNA circuit bridge templates and variants are verifiedfor sequence integrity. Sequence integrity refers to the actualnucleotide sequence as compared to the desired sequence. DNA sequencingmethods will reveal the exact nucleotide sequence of the moleculesintended to be labeled and attached to the MEMS lead surfaces. Thepresent subject matter is sensitive to single base pair mismatches,thus, any sequence variation should be accounted for.

The following describes testing and analysis of biochemical and physicalfeatures of the biological component.

In one example, specific ssDNA molecules are selected, mass produced,and used to bridge the mobile elements of a MEMS circuit. The selectionof the specific ssDNA molecules is based upon a number of biophysicalfeatures such as length, nucleotide composition and sequence,flexibility and mechanical motion, and conductivity parameters. Thecalculated motion and conductivity parameters are verified by atomicforce microscopy (AFM) which can measure specific physical properties(i.e. molecular motion as determined by tip displacement andconductivity) of the ssDNA bridge template and variant ssDNA fragments.AFM tips and stages coated with gold and streptavidin according topublished procedures are bridged by thiol/Biotin end labeled DNA bridgetemplates. AFM tip displacement and material electrical properties aremeasured prior to, during and subsequent to hybridization withcomplimentary and variant ssDNA molecules as input into MEMS devicedesign.

Operational, chemical and temperature environments can be considered forspecific ssDNA bridge templates. For example, reagents to control theeffects of the user-defined operational environment, operationaltemperature, and DNA specific hybridization (pH buffers, salts),denaturation, hydrolysis and nucleotide oxidation can have an effect. Inone example, operational reagents include:

a. Salts, pH, temperatureb. Hydrolysis control: Conductivity through aqueous environments mayinduce hydrolysis that could affect conductivity through the media.Control of this effect through the addition of appropriate reagents.c. Oxidation control: Conductivity through DNA may induce oxidativedamage particularly to the guanine residues. Control of this oxidativedamage through the addition of antioxidants (i.e ascorbic acid, citricacid).d. DNA thermal stability factors (i.e. 0.5-3 molar betains(N,N,N,-trimethylglycine; (Rees et al., Biochem., (1993) 32:137-144).e. Denaturing reagents (i.e. 2-4 molar tetraethyl acetate, urea,chaotropic salts (i.e. trichloroacetate, perchlorate, thiocyanates andfluoroacetates), or glycerol, formamide, formaldehyde, anddimethylsulfoxide (DMSO).f. Hybridization accelerants to enhance DNA to DNA hybridization throughmolecular exclusion phenomenon. Exemplary accelerants include mixturesof acetate salts and alcohols, certain amines (spermine, spermidine,polylysine) 0.1-0.5 molar detergents (dodecyl trimethylammonium bromide,and cetyltrimethylammonium bromide) and specific small proteins such assingle stranded binding protein.

The following describes verification of DNA specificity.

In one example, DNA circuit bridge templates and variants are verifiedfor sequence specificity. Software analysis of the selected DNA fragmentmay demonstrate the specificity of the fragment for one region of onestrain of a targeted biological agent which may be confirmed throughbioagent specificity screening. An example of these methods includesSouthern screening in which various restriction digested fragments ofthe bioagent target genome (and any other suspected related species) areelectrophoretically resolved and transferred to a solid substrate (i.e.nylon or nitrocellulose). The fixed genomic DNA fragments may then beincubated with labeled (i.e. fluorescent or radioactive) DNA bridgetemplate DNA. Under appropriate conditions (i.e. temperature, pH, andsalt concentration) the template DNA will hybridize to a single fragment(assuming the genomic DNA restriction digests did not cut the fragment).Multiple sites of DNA template hybridization to the genomic DNA mayentail modification of conditions in the biodetection device orselection of a new template DNA.

The following describes DNA bridge template end labeling.

In one example, synthesized, PCR amplified, or cloned DNA fragments(selected to bridge MEMS circuit leads) are attached to MEMS surfaces byany of the various methods concerning DNA attachment to organic orinorganic surfaces. In one example, orientation-specific immobilizationis achieved when unique chemical moieties on the DNA bridge templatetermini and MEMS lead surface are cross linked. Commercially availablechemical moiety-specific crosslinkers are generally based onnucleophilic substitution chemistry. This chemistry generally involves adirect displacement of a leaving group by an attacking nucleophile. Inone example, the MEMS circuit leads include leads coated with gold andstreptavidin respectively. In one embodiment, ssDNA bridge templates arecovalently attached to AFM and MEMS surfaces via biotin-streptavidin andthiol-gold bonds. The DNA fragments are 5-prime/3-prime biotin/thiolend-labeled with commercially available kits or by any other means oflabeling or functionalizing the 5′ and 3′ ends of DNA. Attachmentchemistries can include, but is not limited to amino groups (such asN-hydroxy-succinimidyl esters), polyethylene glycols, carbodiimide,thiol groups (such as maleimide or a-haloacetyl), organo-silane groups,or biotin-streptavidin. In one example, DNA fragments are synthesizedwith 5′ and 3′ biotin or streptavidin modified nucleotides, or PCRamplified with biotin/streptavidin labeled primers from genomic orplasmid borne DNA targets.

The following describes an example of MEMS fabrication.

In one example, microelectromechanical systems (MEMS) refers totechnology utilizing small mobile structures constructed on themillionth of a meter (micron) scale. These structures are made throughthe use of a number of tools and methodologies, similar to that used inthe fabrication of integrated circuits (IC). MEMS devices, in oneexample, include combinations of mechanical elements and electricalelements, and, upon fabrication, are placed in a pinned packaging thatallows attachment through a socket on a printed circuit board (PCB).

The following describes MEMS layered construction.

In general, fabrication of a MEMS device involves the deposition of thinfilms of material onto a substrate, the application of a patterned maskonto the material using photolithographic methods and the selectiveetching of the film using the resulting developed mask. Deposition ofthe material onto the substrate (usually silicon wafers) can beaccomplished by chemical reaction-based approaches (chemical vapordeposition, epitaxy, electrodeposition, or thermal oxidation) or byphysical reaction-based approaches (evaporation, sputtering or casting).Each of which varies in speed, accuracy and process cost; the appliedmaterial can be from a few nanometers to about 100 microns. Applicationof the pattern involves placing a photosensitive material on thesurface, locating the patterned mask over the surface (typically withthe aid of alignment marks on the surface and mask), and exposing thephotosensitive material through the mask. Depending on the process used,either the positive or the negative of the exposed material can beremoved, leaving the pattern on the substrate material. Other proceduresincludes preparing the surface, developing the photosensitive film andcleaning the result.

MEMS element manufacture may be performed using micro fabricationtechniques. In one example, lithographic techniques are employed infabrication using semi-conductor manufacturing procedures, such asphotolithographic etching, plasma etching or wet chemical etching, onglass, quartz or silicon substrates.

The removal of materials is typically accomplished through wet etching,in which the material is dissolved away when immersed in a chemicalsolution, or dry etching, in which material is removed in a processessentially opposite physical reaction-based deposition. As with thevarious approaches to deposition, speed, accuracy and cost vary with theapproach. In one example, etching of “deep” pockets from a substrate isperformed with side wall aspect ratios at 50 to 1.

The MEMS device can be fabricated with one or more mobile elements,across which will be attached the template molecule of ssDNA. The mobileelement, for example a cantilever beam, can be constructed so that boththe beam and the substrate beneath the free end of the beam contain atleast one conductive layer. Thus, the circuitry for the device, usingpatterned photolithographic masks, can be constructed using appropriateapplication of insulating and conducting material layers. In oneexample, the geometry allows for flow of sample from one DNA bridgedMEMS to the next and re-circulating to enhance probability of contactand to conserve reagents. One embodiment includes an electronic circuitconstructed on a support composed of such materials such as, but notlimited to, glass, quartz, silicon, and various polymeric substrates,e.g. plastics.

In one example, various insulating layers are provided on the substrate.In one example, solid material amenable to supporting and responding tothe described molecular properties (i.e. conductivity and motion) areused to construct the device. Although the figures in this disclosuremay depict a flat positioning of the circuit, other embodiments includeother orientation (i.e. vertical, etc.).

One example includes additional planar elements(s) which overlay thechannels and reservoirs to enclose and seal to form conduits. Thisadditional planar surface is attached by adhesives, thermal bonding, ornatural adhesion in the presence of certain charged or hydrophilicsubstrates.

In one example, sample collection and preparation is completed outsidethe device. Samples are collected from surfaces using swabs or pads orcollected in air or liquid by aspiration through filters, liquid trapsor chromatography resins. Those samples are prepared by the addition ofthe reagents to disrupt the biological agent, release the targetmolecules and prepare those molecules for sensing by the device. Theprepared sample are then be introduced into the device through a flowchannel, reservoir or duct by syringe, pipette, eyedropper or other suchmanual or automated means.

One example includes air sample acquisition and preparation into thedevice itself for automatic operation through the presence of anon-board fan aspiration system. One example includes automated liquidsample collection and preparation into the device. Disruption of thesamples can be provided by mechanical means, such as sonicationtechniques.

In one example, the sample is delivered through a flow path incorporatedinto the device to the surface of the biochip. The device includesreservoirs of reagents for sample preparation, as well as for systemflushing, device calibration and waste material collection. In oneexample, the device includes means of pumping materials to and fromthese reservoirs. In one example, the device recirculates reagentsthrough the system if no positive sensing event has occurred and thereagent remains of suitable purity.

In one example, oligonucleotide sequences are layered upon the leads toaide in the positioning and orientation of DNA bridge templates. Ingeneral, the oligonucleotide directed hybridization of DNA across acircuit is used to orient and position the single stranded DNA (ssDNA)bridge template. In one example, the ssDNA bridge template is bound tothe MEMS leads via any method of attachment, including thiol or biotinmediated bonds.

Multiple DNA bridged MEMS circuits can be positioned on a single chip ina matrix or array geometry in order to enable simultaneous detection andidentification of multiple pathogens from the same sample. In oneexample, the matrix includes multiple repeats of identical DNA bridgedMEMS in order to enable concentration measurement of target DNAmolecules as a function of the number of ‘stimulated’ circuits pervolume of sample.

The following describes biological bridging of MEMS mobile elements.

After the physical MEMS device containing the mobile elements and thecircuitry is fabricated, the single ssDNA molecule of interest (thetemplate molecule) is attached to the device. In one example have acantilever beam, the ssDNA is attached from the free end of thecantilever to the substrate base beneath the cantilever. In one example,the surfaces are prepared such that the functionalized ends of thetemplate ssDNA will attach to the surface. The ssDNA is functionalizedwith a thiol group on one end (that has a high affinity for a goldsurface) and biotin on the other end (that has a high affinity for astreptavidin-coated surface). Thus, if gold is used on the conductor onthe bottom surface of the cantilever, the thiol-functionalized end ofthe ssDNA will attach to it. A gold surface on the substrate below thefree end of the cantilever will also be exposed. Before introduction ofthe ssDNA template to be bound, biotin is electrostatically deposited onthe gold surface on the substrate. Streptavidin is introduced over thewafer, which bonds to the biotinylated surface on the substrate.Accordingly, the surfaces of the MEMS device are prepared to bind thessDNA template.

The following describes electrostatic trapping of a bridged moleculetemplate which, in one example, includes attachment of a single ssDNAmolecule across the gap between the free end of the cantilever and theprepared substrate base beneath it. In one example, an electricalpotential is applied across the gap, in series with a large resistor.The ssDNA molecule is attracted to the resulting electrical field. Whenin close proximity, the biotin-streptavidin bonds on the substrate baseare formed, and the gold-thiol bonds are formed on the free end of thecantilever. As soon as one molecule attaches in this manner, thepotential across the gap is vastly reduced due to the resistance inseries in the circuit. Thus, only one ssDNA molecule will attach at eachsite. Field assisted attraction of ssDNA to MEMS lead arms—device toaide in single molecule attachment. Electrostatic trapping of singleconducting nanoparticles between nanoelectrodes. Appl. Phys. Lett.71(9).

The following describes removal of excess template molecules.

In some cases, even though only one strand has attached across the gap,a number of ssDNA may be tethered to either the gold or the biotinilatedsurface. These “strays” have the potential of undesirably binding targetpathogen ssDNA sequences. In one example, the device is treated with anexonuclease, to remove all ssDNA not tethered at both ends, thuseliminating the potential of binding events at other than sensor sites.

In one example, the system incorporates additional mobile elements,bridged with either synthetic or biological molecules, that act asreference or baseline controls for the elimination of mechanical,electrical or chemical background effects such as temperature, pressure,motion, stray voltage, induced electrical fields, and/or sample chemicalcontaminants. In one example, a device includes thousands of sensor andreference sites on one MEMS chip. The sensor sites may all includebiological elements to detect the presence of a single bioagent, or mayinclude a variety of biological elements to enable simultaneousdetection of numerous bioagents on a single biochip.

The following describes integration of the MEMS circuit into signalamplification, processing, and display systems. Measuring current in thenano-amp range entails integrated circuit amplifiers. In one example,multiplexing and integrated circuit (IC) amplifiers and otherelectronics and processing are used to display the results of thesensing events. An integrated circuit is used to amplify analog signalsfrom the MEMS chip and convert them into digital signals. In oneexample, IC fabrication incorporate the IC into packaging that allowspinned attachment of the IC to a printed circuit board (PCB). Inaddition to providing attachment of the MEMS and IC chips, the PCBincludes a main processor to perform calculations and control electricaloperations on the PCB. The PCB includes an electrical interface for thedisplay and the battery, as well input/output to the menu buttons. Inone example, the processor is programmed to use the digital signalsoutput from the IC to provide display. The user interface includesdirect controls of the display, and controls to set parameters thatdetermine the display characteristics, the threshold detection values,battery level, on/off and bioagent molecule purging control. In oneexample, the PCB, display, user interface, battery and input/output areintegrated into a plastic or metal housing.

The following describes testing and analysis of an exemplary system. Oneexample entails sample collection, processing, and delivery to theelectronic circuitry.

a. Sample Collection: The procedure for air, liquid, or solid samplecollection are based on the target molecule source and instrumentworking environment. For example, particles of appropriate size, mass,or charge may be isolated and collected by filtration and/or massspectrometry methods. Chemical or biological agents trapped on filterscan be eluted by sample preparation reagents and delivered to theinstrument. In one example, instrument aspiration technology is employedto draw or force air samples through sample preparation reagents thatsubsequently are delivered to the detection chip.b. Sample Preparation: In one example, air, liquid, or solid samples areprepared externally to the detection device or internally via automaticsample preparation technologies. Specific steps and reagents for samplepreparation depend upon the source and target molecules to be detectedand identified. Chemical, thermal, and/or mechanical means are used torupture biological cell contents and release target molecules. Similarmeans are used to prepare previously prepared organic or inorganicsources of target molecules. In general, disruption of biological cellsrequires detergents that solubilize lipid membranes, enzymatic digestionof proteins associated with cell membranes or target molecules, andvarious denaturants that modify or otherwise prepare the targetmolecules for detection and identification. Mechanical means includesonication or agitation, alone or in the presence of, disruptive beads.In one example, filtration or chromatography methods are used to purifythe target molecules based upon size, hydrophilicity, charge, or ligandaffinity. In one example, the system is resistant to target sourceassociated components and other environmental contaminants (i.e. salts,dusts, solvents or reagents specifically added to inhibit properdetection or identification. In one example, the system is sensitivetrace amounts of target molecule associated with the sample. In oneexample, the system detects and identifies specific DNA fragments foundin, on the surface of, or other wise associated with the DNA source(i.e. microbe, animal cell, virus). In one example, the double strandedDNA is fragmented and denatured.c. Sample delivery to microchip.d. Detection, identification and discrimination occurs.e. Result displayed on device.

Exemplary applications for the present system include real timedetection, identification, discrimination, and concentration measurementof components derived from sources including, but not limited toanimals, bacteria, viruses, fungi, plants, archaea, found in soil,water, or air. Exemplary components include, but are not limited toorganic (i.e. composed of nucleic acids, amino acids, or carbohydrates,etc.) or inorganic (i.e. metals, inorganic phosphates, etc.) related tohuman, plant, or animal pathogens, components and sources of concern tofood safety, components and sources of concern to medical diseases,genetic sequences associated with predisposition of diseases,pre-symptomatic diagnosis of diseases in plants and animals, laboratorydiagnostic tool of listed components or sources, a laboratory tool tomonitor gene expression of specific RNA and identification of specificanimals or persons through polymorphism ID.

In addition to DNA-DNA interaction, other alternatives are contemplated,including:

Protein—Protein

1) Prion protein interaction with other Prions. Bovine spongiformencephalopathy (BSE, also known as mad cow disease), is aneurodegenerative disease in cattle and ingestion of infected meatproducts causes Creutzfeldt-Jakob Disease (CJD and vCJD) in humans.Variations of BSE have been identified in animal species and all havebeen classified as transmissible spongiform encephalopathies (TSEs). BSEin cattle, or CJD in humans, results when a neural protein called aprion changes shape from its normal form to a misfolded infectious form.The mis-folded infectious prions then induce other prion proteins toalso mis-fold. The present system can detect physical conformation of anormal prion to the infectious form. In one example, a normal prionprotein is attached via surface exposed cysteine or histidine residuesto gold, nickel or platinum coated MEMS surfaces.2) Antibody—Antigen interaction. In one example, the mobile elements ofa MEMS circuit are bridged with a naturally produced or syntheticrepresentation of the antigen binding site of an antibody that isspecific to an antigen from a particular biological or inorganic agent.In one example, the amino acid molecule representing the antigen bindingsite is attached to the mobile MEMS surfaces via similar chemistry notedabove for prions. Interaction of bio-agent antigens with bridged antigenbinding sites induces a structural change in the bridged element thuscreating a measurable signal.

Protein—Carbohydrate (Glycoprotein Formation)

1) interactions between extra cellular carbohydrate epitopes andreceptor proteins can be detected and analyzed. Examples of suchbiological processes include viral and bacterial infections. Oneexemplary model is the Jack bean (Canavalia ensiformis) proteinconcanavalin A (con A) with mannose sugars (Acta Crystallogr., Sect. D50 pp. 847 (1994)). One example includes bridging the mobile elements ofa MEMS circuit with Con A via histidine or cysteine residues. Glucosecontaining samples bind and alter the dimensional configuration of theCon A protein thus generating a signal to the system. The present systemincluding such a circuit can detect the presence and concentration ofglucose residues in the case of diabetes control.2) The glycolipid globotriaosyl ceramide, expressed on kidney cellsurfaces acts as the receptor to the Shiga-like toxin 1 (SLT1), a memberof the two-component bacterial toxins, through binding interactionsbetween the protein's pentameric ‘B’ binding subunit.

Carbohydrate—Carbohydrate

Cell to cell interactions and cell adhesion forces are sometimesassociated with carbohydrate interactions with other carbohydrates orglycoproteins (J Cell Biol. 2004 May 24; 165(4):529-37. 2004 May 17).Glycosphingolipid (GSL) co-interaction appears to play a role in mousemelanoma cell adhesion. One exemplary system includes the creation ofglycoprotein structures with GSL binding sites for the purpose ofmonitoring cancer cell growth.

In one example, a chemical and biological detection/identificationsystem entails sample collection, sample processing and delivery, sampleanalysis technology, and signal processing and output.

Strength of a DNA strand and length are dependent upon base composition,sequence, and environment. On average, the diameter of dsDNA is 20Angstroms (Å), and the distance between adjacent nucleotides 3.4 Å orapproximately 34 Å for one full helical rotation. The dsDNA helixdemonstrates two grooves; the minor groove (˜12 Angstroms) and majorgroove (˜22 Angstroms). The distance between adjacent nucleotides ofssDNA however is approximately 5.84 angstroms.

Molecular Contraction

The first physical phenomenon is related to the helical shape assumed bydouble stranded DNA (dsDNA). A single strand of DNA (ssDNA) is generallya linear physical structure of a length equal to approximately 5.84Angstroms per nucleotide base. (The individual building blocks (bases)comprising a DNA strand are guanine (G), adenine (A), thymine (T), andcytosine (C)). The alignment and bonding of one strand of DNA with itscomplimentary strand (a process referred to as hybridization), resultsin a helical-shaped dsDNA structure with a reduced distance betweennucleotide bases of 3.4 Angstroms. Therefore whereas 50 bases of ssDNAis approximately 292 Angstroms, the same number of nucleotides of dsDNAis only 175 Angstroms (17.5 nm), or an expected average reduction in DNAlength of approximately 40% (dependent upon base composition, sequence,and environment). This reduction in length is a consistent andphysically measurable event.

Additionally, the amount of overall change in length of the molecule isrelated to the degree of match between the first (template) ssDNA andthe second (compliment or target), attaching strand. Under appropriateconditions, less than perfectly matched DNA strands will also hybridize.However, there is a proportionately lesser effect on length reduction.Thus, if the change in length is measured, and the maximum change inlength due to a perfect match is known, the degree of variation of thegenetic sequence between a target ssDNA and an introduced ssDNA can bedetermined. Environmental conditions that demand exact matches includelow salt conditions and high temperatures (20 C A&T, 40 C G&C).Conversely, hybridization between in-exact matched DNA strands (orgenetic variants) is possible by raising the salt conditions andlowering the temperature.

The interaction of one ssDNA molecule with another and the resultingchanges in physical conformation is critical to the function of theinvention. The overall strength of strand-to-strand and subunit linkbonding is a result of the combined attractive forces between individualunits. These attractive forces include hydrogen bonding, base stackinginteractions, and hydrophobic interactions that force bases into theinterior and phosphates to the exterior. It is also important to realizethat the exact measure of bonding energy is dependent upon neighboringnucleotides and nature of the environment (pH, temperature, ionicstrength, etc.). Hydrogen bonding adds 4-7 kcal/mole, base stacking adds3.8-14.6 kcal/mole, and the covalent bond energies of phosphodiesterlinkages (80-100 kcal/mole) (references). Experimental and theoreticalstudies confirm that the average base composition and sequence dsDNAtensile strength is approximately 5×10-12 Newtons (kg/sec2)(references). This force corresponds roughly to the weight of a singlebacterium; nevertheless the techniques just mentioned are delicateenough to apply such forces accurately.

Conductivity

A second physiological phenomenon related to the recombination of twomatching ssDNA is that there occurs a marked increase in conductivity ofthe ssDNA subsequent to hybridization. A number of research studies haveproven that ssDNA is capable of conducting electricity. The conductivityof the ssDNA is highly dependent on the makeup of the genetic sequence,with guanine and cytosine (G and C) tending to act as conductors whileadenine and thymine (A and T) tending to act more as insulators(references).

The increase in conductivity subsequent to hybridization can be as muchas 100× that of ssDNA for appropriately G-C rich sequences. Debateexists in the literature as to the mechanism that allows this remarkableincrease, be it electron tunneling through the base pair region orelectron hopping in the sugar phosphate backbone; regardless of themechanism, the increase is measurable and well above any signal-to-noiseconcerns.

As with the change in molecule length, the increase in conductivity isproportional to the degree of match between a target ssDNA and apotential matching ssDNA. The greater the mismatch between the ssDNAmolecules, the less the increase in conductivity subsequent tohybridization.

Voltage Induced Denaturation

A third physiological phenomenon is related to the separation of a dsDNAinto the two complimentary ssDNAs. Southern hybridization is awell-proven laboratory approach to control the hybridization anddenaturation of DNA molecules (references). By controlling theenvironmental variables such as salinity and temperature, one can forcehybridization or denaturation of the DNA molecules. Denaturation canalso be effected by the passing of sufficient current through the dsDNA.Again, the ultimate mechanism is not completely understood; however, thephenomenon has been repeatedly observed (references).

As with the changes in molecular length and conductivity, the currentrequired to force denaturation of the dsDNA into the two component ssDNAis proportional to the degree of match between the component ssDNAs. Thegreater the match, the greater the current required to result indenaturation.

DNA Template Production

Bacillus subtilis Genomic DNA preparation: Bacillus subtilis (Ehrenberg)Cohn strain 168, (American Type Culture Collection (ATCC) #27370) wascultured in 100 ml sterilized ATCC media #265 composed of 12.5 g heartinfusion broth (BD #238400), 5.4 g nutrient broth (BD #234000), and 2.5g yeast extract (BD #212730) per liter. The cultures were grown for 15hours at 30° C. with shaking at 140 rpm. Genomic DNA was purified fromthe cultures according to an adaptation of a standard procedure (Marmur,J. 1961. A procedure for the isolation of deoxyribonucleic acid frommicroorganisms. J. Mol. Biol. 3:208-218). Briefly, 100 ml bacilluscultures were centrifuged at 4000×g for 10 minutes. Pellets wereresuspended and incubated for 1 hour at 37° C. in 9.5 ml TE (10 mM Tris(tris hydroxyl-aminomethane EM #9210), 1 mM EDTA (ethylene diamidetetra-acetic acid EM #4010)); 0.5 ml 10% SDS (sodium dodecyl sulfateEM#DX2490-2); and 50 microliters 20 mg/ml proteinase K (EM #24568-3).After incubation, 1.8 ml of 5M NaCl (sodium chloride VWR #6430-1) isadded and the solution mixed thoroughly followed by the addition of 1.5ml CTAB/NaCl solution (10% CTAB (hexadecyltrimethyl ammonium bromide VWR80501-950) in 0.7 M NaCl)) and incubated at 65° C. for 20 minutes. Thesolution is extracted with an equal volume of chloroform (EM#CX1054-6)/isoamyl alcohol (Calbiochem #80055-544) and spun for 10minutes at 6000×g at 22° C. The aqueous phase was extracted with phenol(EM #PX0511-1)/chloroform/isoamyl and spun for 10 minutes at 6000×g at22° C. DNA in the aqueous phase was precipitated by the addition of 0.6volumes of isopropyl alcohol (VWR 3424-7) and spun for 10 minutes at6000×g at 4° C. The precipitate was washed with 70% (v/v) ethanol andresuspended in 4 ml TE. The concentration was determined byspectrophotometer absorbance at 260 nm, and adjusted to 100 μg/ml. 200μl of ethidium bromide (EM #4310) and 4.3 g of CsCl (cesium chloride EM#3030) were added per 4 ml of DNA. The solution was spun for 4 hours at300,000×g at 15° C. The genomic DNA band was visualized by UV light andremoved by syringe needle. The ethidium bromide was extracted withCsCl-saturated isopropanol, and the CsCl removed by overnight dialysisin 2 liters TE at 4° C. The DNA was precipitated with 0.6 volumesisopropyl alcohol and stored at −70° C.

PCR Amplification of Bacillus subtilis 16S rRNA:

The 16S rRNA gene of B. subtilis was PCR amplified from the genomic DNAprepared above according to published methods (H.-J. Bach, 1, D.Errampalli, K. T., Leung, H., Lee, A., Hartmann, J., T. Trevors, and J.C. Munch. 1999. Specific Detection of the Gene for the ExtracellularNeutral Protease of Bacillus cereus by PCR and Blot Hybridization.Applied and Environmental Microbiology, p. 3226-3228, Vol. 65, No. 7).Amplification of DNA was carried out with the GeneAmp PCR System 9600(Perkin-Elmer, Norwalk, Conn.). 50 μl samples contained 50 ng oftemplate B. subtilis genomic DNA, 25 picomole of each primer (Forward:5′-gggtttgatcctggctcag-3′; Reverse: 5′-acggttaccttgttacgactt-3′), 0.2 mMdeoxynucleotide triphosphates (Boehringer, Mannheim, Germany), 2 unitsof Taq/AmpliTaq® DNA polymerase (Promega), 5 μl of 10× reaction buffer(EM), and 3 mM MgCl₂ (EM). The PCR program was as follows: hot startcycle of 94° C. for 5 min and 80° C. for 4 min; one cycle of 94° C. for2 min, 64° C. for 1 min, and 72° C. for 2 min; 30 cycles of 94° C. for30 seconds, 64° C. for 30 seconds, and 72° C. for 45 seconds; and afinal extension at 72° C. for 10 minutes. Amplified PCR products wereresolved by gel electrophoresis with 0.8% agarose (Promega LMP #V2831)in TAE buffer (40 mM Tris-acetate [pH 7.6], 1 mM Na₂EDTA). Theapproximately 1500 bp PCR product was excised, and extracted from theagarose using AgarACE® (Promega) digestion method. (Note: the primersnotes above have been specifically designed by Dr. Albert as tools toPCR amplify the 16S rRNA nucleotide sequence from numerous bacteria).

Cloning of Bacillus subtilis 16S rRNA:

The 16S rRNA PCR product produced in the step above was ligated intoplasmid cloning vector pGem®-T Easy (Promega) according tomanufacturer's recommended procedure. Briefly, 75 ng PCR product wasadded to 5 μl 2× rapid ligation buffer (Promega), 1 μl (50 ng) vectorDNA, and 1 μl (3 Weiss units) T4 DNA ligase. The reaction solution wasincubated at 22° C. for one hour. The ligation reaction product wastransformed into JM109 competent cells (Promega) according to thefollowing procedure: 2 μl of ice cold ligation reaction was gently addedto 50 μl of ice cold competent cells in a sterile 1.5 ml tube. The tubewas incubated on ice for 20 minutes, followed by 50 seconds at 42° C.,and returned to ice for 2 minutes. 950 μl of 22° C. sterile SOC mediumwas added and the tubes incubated at 37° C. for 1.5 hours shaking at 150rpm. The transformed cells were plated on LB/ampicillin/IPTG/X-Galplates. And the plates incubated at 37° C. for 20 hours. White colonieswere subsequently screened for inserts by the plasmid miniprep procedureoutlined below.

Plasmid Miniprep Procedure:

Plasmids containing inserts of B. subtilis 16S rRNA nucleotide sequencewere quickly purified from the JM109 E. coli hosts by a modification ofthe technique of Blin & Doly in Nucleic Acids Research 7:1513-1523(1979). Twenty white colonies, representing candidate insert/vectortransformed clones, were each picked by sterile pipette tip into 2 mlLB/ampicillin broth in a sterile capped test tube and incubated for 16hours at 37° C. shaking at 200 rpm. The cultures were each added to asterile 1.5 ml microcentrifuge tube and centrifuged at 4000×g for 5minutes at 4° C. The pellets were resuspended in 180 μl Solution I plus20 μl 5 mg/ml lysozyme and incubated at 22° C. for 5 minutes. 400 μl ofsolution II was added by inversion×5 and the solution was incubated onice for 5 min. 300 μl ice cold solution III was added and the tubecontents vortexed and incubated on ice for 10 minutes. The samples werecentrifuged at 10,000×g for 2 minutes at 22° C., and the supernatanttransferred to a new sterile 1.5 ml microcentrifuge tube containing 500μl (0.6 volumes) of isopropanol to precipitate the DNA. The samples werevortexed and centrifuged at 10,000×g for 5 minutes at 22° C. and thepellets were resuspended in 200 μl of TE.

Screening Transformants for 16S rRNA Gene Inserts:

5 μl of the plasmid preparation were restriction digested with Not I(Promega) according to manufactures direction, and plasmid and excisedinsert fragments were resolved by 1% agarose electrophoresis to identifycolony isolates containing the desired pGem-B. subtilis rRNA plasmidconstructs. Clone candidates identified by electrophoretic analysis asharboring the appropriate plasmid construct were cultured in 500 mlLB/ampicillin media, aliquots were stored in 70% glycerol at −70° C.,and large scale plasmid preps were conducted to establish a stock ofcultures and DNA.

Alternative approaches toward generating the same 121 bp bridgetemplate: Two alternatives toward generating the identical 121 bpnucleotide sequence are provided below.

-   -   1) Subcloning from B. subtilis DNA. Frequently, cloned fragments        of microbial DNA can be obtained from personal or commercial        sources. Plasmids containing large inserts of B. subtilis DNA        that include the desired 121 bp fragment could be digested with        the restriction enzymes Aat II and Sph I. The digest would        release a 171 bp fragment that could be cloned into any        appropriate cloning vector such as the pGem-T (Promega) Aat        II/Sph I sites. The desired 121 bp fragment could be subcloned        from this plasmid according to the PCR procedure indicated        above.    -   2) Synthesis of the desired bridge templates. The desired        oligonucleotide bridge templates may be synthesized on any        commercially available system such as an ABI 392 DNA        synthesizer. Standard phosphoramidite chemistry would be        utilized resulting in a dimethoxy trityl protecting group on the        5′ end. The molecules would be purified by C18 reverse phase        HPLC (25 mM NH 4 OAc, pH 7, 5-25% CH 3 CN over 30 min) followed        by deprotection in 80% acetic acid for 15 min. Following        deprotection, the oligonucleotides would be purified a second        time on the same C18 column by reversed-phase HPLC (25 mM NH 4        OAc, pH 7, 2-20% CH 3 CN over 30 min). Synthesized DNA        quantities would be determined UV-visible absorption        spectroscopy using the following extinction coefficients for        single-stranded DNA: (260 nm, M-1 cm-1) adenine (A)=15,000;        guanine (G)=12,300; cytosine (C)=7400; thymine (T)=6700. Since        most synthesis procedures loose fidelity beyond 70-90 bases, the        121 bp bridge template discussed here would be synthesized in at        least two fragments. Specifically, as shown in step 1 of the        research plan, four ˜60 base single stranded nucleotides would        be synthesized, and hybridized and ligated to each other in the        appropriate manner. The product would then be ligated into a        cloning vector.

Preparation of 121 bp Circuit Bridge Template by PCR Amplification:

The 121 bp segment of the B. subtilis 16S rRNA gene was PCR amplifiedfrom the pGem-B. subtilis rRNA plasmid construct. 50 μl samplescontained 50 ng of Sal I digested template plasmid DNA, 25 picomole ofeach primer (Forward: 5′-CGAGCGGCCGCCTGGGCTACACACGTGC-3′; Reverse:5′-CGACCGCGGCCAGCTTCACGCAGTCG-3′), 0.2 mM deoxynucleotide triphosphates(Boehringer, Mannheim, Germany), 2 units of Taq/AmpliTaq® DNA polymerase(Promega), 5 μl of 10× reaction buffer (EM), and 3 mM MgCl₂ (EM). ThePCR program was as follows: hot start cycle of 94° C. for 5 min and 80°C. for 4 min; one cycle of 94° C. for 2 min, 64° C. for 1 min, and 72°C. for 2 min; 30 cycles of 94° C. for 30 seconds, 64° C. for 30 seconds,and 72° C. for 45 seconds; and a final extension at 72° C. for 10minutes. Amplified PCR products were resolved by gel electrophoresiswith 1.5% agarose (Promega LMP #V2831) in TAE buffer (40 mM Tris-acetate[pH 7.6], 1 mM Na₂EDTA). The approximately 121 bp PCR product wasexcised, extracted from the agarose using AgarACE® (Promega) digestionmethod. The purified product was ligated to the Not I/Sac II site ofpGem vector, transformed in JM109, and 121 bp insert containing plasmidwas produced as described above.

DNA Bridge Template Specificity Verification:

The 121 bp B. subtilis fragment cloned by the procedure described abovewas verified for sequence integrity through commercially availablesubcontracted DNA sequencing services. It was determined that the 121 bpinsert nucleotide sequence was:5′-ctgggctacacacgtgctacaatggacagaacaaagggcagcgaaaccgcgaggttaagccaatCccacaaatctgttctcagttcggatcgcagtctgcaactcgactgcgtgaagctgg-3′, and is anexact match to 16S rRNA Bacillus subtilis subspecies subtilis strain 168(Entrez PubMed accession #NC000964).

The specificity of the 121 bp insert was verified through standardSouthern screening against genomic DNA of Bacillus subtilis and otherBacillus species (i.e. B. globigii, B. cereus, B. subtilis, B.thuringiensis) purchased commercially from the American Type CultureCollection. Southern hybridization screening involved the followingprocedure. Bacillus species genomic DNA, generated as described above,was restriction digested with restriction enzymes Hind III, EcoR I, andPst I which do not digest the 121 bp insert. The fragments generated bythe digests were resolved on 0.8% agarose in TAE and stained withethidium bromide. The gel was UV treated at 260 nm for 5 minutes on atransilluminator, subsequently soaked in 0.2 M HCl for 7 minutes. Thegel was then soaked in base solution (1.5M NaCl, 0.5M NaOH) for 45minutes, followed by the neutralizing solution (5 M Tris-HCl, 3M NaCl,pH 7.4) for 90 minutes. In standard Southern configuration (Southern, E.M. (1975) Detection of specific sequences among DNA fragments separatedby gel electrophoresis. J. Mol. Biol. 98, 503-517). Briefly the treatedgel is sandwiched between absorbent Whatman 3MM filter paper and a DNAbinding nitrocellulose (SS), such that 20×SSPE (3 M NaCl, 0.2 M NaH2PO4,20 mM EDTA, pH 7.0) is wicked through filter paper, and through the gelas it transfers the gel DNA onto the binding membrane. The genomic DNAwas allowed to transfer for 16 hours at room temperature. The membranewas removed and soaked in 5×SSPE for 30 minutes and baked in an 80° C.vacuum oven a few hours until the filter was dry. The membrane was thenprobed for fragments that would hybridize to the above 121 bp clonedtemplate fragment labeled according to manufactures directionAlkPhos®-DIRECT (Pharmacia). Color development of the probed membraneclearly indicated that the probe was specific to B. subtilis, and toonly a single site within the B. subtilis genome.

Generation of Point Mutant Variants:

Genetic variants of the 121 bp nucleotide sequence were created bypublished methods (Molecular Biology: Current Innovations and FutureTrends. Eds. A. M. Griffin and H. G. Griffin. ISBN 1-898486-01-8. 1995Horizon Scientific Press, PO Box 1, Wymondham, Norfolk, U.K).Specifically, 0.5 pmole pGem-B. subtilis plasmid template DNA was addedto a PCR cocktail containing, in 25 ul of 1× mutagenesis buffer: (20 mMTris HCl, pH 7.5; 8 mM MgCl2; 40 ug/ml BSA); 20 pmole each of T7 and SP6primers (Promega), 250 uM each dNTP, 2.5 U Taq DNA polymerase, 2.5 U ofTaq Extender (Stratagene). The PCR cycling parameters were 1 cycle of: 4min at 94° C., 2 min at 50° C. and 2 min at 72° C.; followed by 5-10cycles of 1 min at 94° C., 2 min at 54° C. and 1 min at 72° C. Theparental template DNA and the linear, mutagenesis-primer incorporatingnewly synthesized DNA were treated with DpnI (10 U) and Pfu DNApolymerase (2.5 U). This resulted in the DpnI digestion of the in vivomethylated parental template and hybrid DNA. Pfu DNA polymerase removedthe Taq DNA polymerase-extended base(s) on the linear PCR product. Thereaction was incubated at 37° C. for 30 min and then transferred to 72°C. for an additional 30 min. 115 ul mutagenesis buffer containing 0.5 mMATP was added and the solution mixed. 4 units T4 DNA ligase was added to10 ul of the solution in a new microfuge tube and incubated for 90 minat 37° C. The solution is transformed into competent JM109 E. coli asindicated above and plated on LB/ampicillin for 16 hours at 37° C.Plasmid DNA was generated from individual isolates and the nucleotidesequence determined as indicated above. Isolates demonstrating 2%, 19%,and 35% base mutation were saved for further study.

End Labeling of 121 bp Templates:

DNA bridge templates will be covalently attached to AFM and MEMSsurfaces via biotin-streptavidin and thiol-gold bonds. The plasmidcontaining the 121 bp 16S rRNA B. subtilis fragment was restrictiondigested with Not I and Sac II to release the insert which was gelpurified on 0.8% LMP agarose in TAE buffer as described above. The5′-ends and 3′-ends of the molecules were respectively labeled withthiol and biotin chemistry using commercially available (Pierce #89818)end-labeling kits and according to published procedures (B. A. Connollyand P. Rider, Nucleic Acids Res. 13, 4485 (1985). AND A. Kumar, S.Dvani, H. Dawar, G. P. Talwar, ibid. 19, 4561 (1991).

Measurement of DNA Physical Properties:

Atomic force microscopy (AFM) is typically used to assess the topographyof a surface at the molecular level. The AFM system includes acantilever arm with a sharp tip protruding orthogonal to thelongitudinal axis of the arm. The arm is lowered until the tip comesinto contact with the surface, and then is pulled along the surfacemeasuring changes in surface dimensions. The movement of the cantilevertip is measured; the process is repeated over enough of the samplesurface to characterize the topography. Most commonly, the tipdeflection is measured using a reflected laser approach.

In this work, AFM was used for sake of either measuring the forcerequired to break the bonds along the axis of a single or doublestranded DNA molecule, to measure the displacement of the AFM tip as aresult of the motion of bound DNA molecules.

Experimental measurements of resistance to force applied to a moleculetethered between an AFM tip and stage: A molecule loosely tetheredbetween tip and stage is initially compressed in standard AFM fashionuntil a positive force is recorded. As the tip is subsequently liftedfrom the surface, the molecule becomes taut resulting in a negativeforce recording until the distance between tip and stage exceeds maximummolecular length at which point the molecule breaks.

Atomic force microscopy (AFM) was used to accurately measure specificphysical properties (i.e. displacement and conductivity) of the B.subtilis 121 bp insert and variant DNA fragments. The AFM was operatedaccording to prescribed chemistry and methodology. AFM tips and stageswere coated with gold and streptavidin according to publishedprocedures, and the thiol/Biotin end labeled DNA bridge templatesgenerated above were attached (R M Zimmermann and EC Cox. 1994. DNAstretching on functionalized gold surfaces. Nucleic Acids Research, Vol22, Issue 3 492-497). Prior to attachment, the end-labeled DNA thiolgroup was deprotected overnight with 0.04 M DTT, 0.17 M phosphatebuffer, pH 8.0. Repeated extractions with ethyl acetate to remove excessDTT was performed just prior to attachment in 10 mM HEPES, 5 mM EDTAbuffer, pH 6.6. Gold treated AFM tips were submerged in the DNA solutionfor 2 hours at room temperature and dried under a nitrogen stream. TheDNA-bound AFM tips were mounted in the AFM, and the reaction chamberflooded with SPE (0.1M sodium phosphate pH 6.6, 1 mM EDTA, and 1M sodiumchloride) to allow for the formation of covalent biotin-streptavidinbonds.

AFM tip displacement and material electrical properties were measuredprior to, during, and subsequent to hybridization with complementary andvariant ssDNA molecules. Reagents that controlled hybridization (pHbuffers, salts), denaturation, hydrolysis and nucleotide oxidation wereexamined.

Experiment concerning tip displacement from fixed state: The length of asingle strand of tethered DNA is reduced as a result of hybridizationwith its complimentary strand. Under these experimental conditions, thelength reduction of the tethered ssDNA results in a measurabledisplacement of the AFM tip toward the stage.

Results

This work described here actually encompassed molecular and AFM researchon approximately 80 molecules ranging in size from 83 bp to 2854 bp inlength. The DNA was derived from plasmid vectors, lambda virus, E. coligenome, and B. subtilis genome DNA. Although the most intensive studieswere conducted on the 121 bp fragment described above, the results weresimilar across all molecules. Initial studies measured the reduction oflength of the single strand of 121 bp fragment attached at both ends tothe AFM tip and stage according to methods discussed earlier. AFM tipdisplacement was observed within seconds of pipetting 4-5 μl of dilute(1-2 molecules per μl) single stranded 121 bp fragments, or denaturedplasmid containing the 121 bp insert. FIG. 4 shows how the 121 bpfragment reduced in length by approximately 10 nm.

The exact length of a strand of DNA is dependent upon base composition,sequence, and environment. On average, the diameter of dsDNA is 20Angstroms (Å), and the distance between adjacent nucleotides is 3.4 Å orapproximately 34 Å for one full helical rotation. The dsDNA helixdemonstrates two grooves; the minor groove (˜12 Angstroms) and majorgroove (˜22 Angstroms). The distance between adjacent nucleotides ofssDNA however is approximately 5.84 angstroms. Therefore whereas 121bases of ssDNA is approximately 701 Angstroms, the same number ofnucleotides of dsDNA should be approximately 411 Angstroms, or anexpected average reduction in DNA length of approximately 40%.Therefore, if the 121 bp strand tethered in the AFM were allowed totwist freely, the tip should have been displaced by as much as 29 nm.

The separate introduction of DNA molecules that differed from theparental nucleotide sequence by 2%, 19%, and 35% (variants) demonstrateda measurable difference in tip displacement. If AFM tip displacement inthese studies was due to double strand DNA helical formation with alength less than that of the single strand DNA, then it would followthat hybrid molecules composed of less complementary strands woulddemonstrate less tip displacement.

FIG. 4 illustrates the 121 bp DNA bridge template was tethered, and heldat slight tension between AFM tip and stage as discussed in the text,for a time prior to approximately 15 seconds. The tip, held at a steadystate position of approximately 71 nm moved approximately 10 nm uponintroduction of the template's complementary DNA strand. Separateintroduction of molecules that varied from the parental by 2%, 19%, and35% resulted in a measurable difference in tip displacement. Graph linesdepict less than 0.3% deviation over 5 measurements each.

AFM cantilever surfaces were gold coated to allow the conductance ofelectrical current through molecules of study. By applying a potentialbetween the cantilever and the stage, a corresponding current wasmeasured through the bridged 121 bp ssDNA template. For an appliedvoltage of approximately one volt, the current measured through thessDNA template was approximately 0.3 nA. When a perfectly complimentarytarget ssDNA was introduced the measured current at the same voltagerose to approximately 2.1 nA.

These results confirm the behavior related to ssDNA/dsDNA conductivitydiscussed earlier. The conductivity of the DNA molecule was alsoconfirmed to be dependent on the composition and sequence of the DNAmolecule. Specifically, adenine (A) and thymine (T) nucleotides act asinsulators whereas guanine (G) and cytosine (C) nucleotides are betterconductors.

Similar results occur when target ssDNA strands are introduced that arean engineered variant with a known degree of variation from thetemplate. The same variant target ssDNA molecules used in thedeformation studies were introduced, with the conductivity responsemeasured accordingly. Of note is the high degree of proportionalitybetween the conductivity increase of the molecules upon hybridizationand the degree of mismatch of the template and target ssDNA strands,providing experimental proof of the specificity phenomenon outlinedearlier. The results were consistent whether the variation occurred onone region of the genetic sequence, or was spread out over a number ofdifferent locations along the sequence of the target.

Once the amount of conducted current was measured through the dsDNA, theapplied voltage was manually increased across the AFM cantilever and thesubstrate, resulting in increased conductance through the dsDNA. Thevoltage was increased until denaturation of the dsDNA occurred. A plotof results for such experiments are shown in FIG. 6. At the point ofdenaturation, the current conducted dropped back down to the levelassociated with ssDNA.

From FIG. 6, there was a high degree of proportionality between theamount of current required to force denaturation and the degree ofmismatch of the template and target ssDNA strands. As with the priorstudies, the results were consistent whether the variation occurred onone region of the genetic sequence or was spread out over a number ofdifferent locations along the sequence of the target.

Another experiment conducted with the AFM involved increasing thevoltage to force denaturation, and then reducing the voltage back tosensing levels to allow another hybridization to occur. As can be seenin FIG. 7, the AFM successfully performed a number of sensing events,and validated the use of the current sensing of hybridization/forceddenaturation by increased current as a means of resetting the biosensor.Of note in FIG. 7 is the consistency of the measured current, bothduring the ssDNA and after hybridization (dsDNA) states, throughout themultiple sensing events. While the experiment depicted in FIG. 7 showsfour discrete sensing events, a number of the experiments were actuallyconducted through hundreds of sensing events, with no notabledegradation of the signal and no significant change in the measuredcurrents before and after sensing.

The AFM allows investigation and verification of the phenomena outlinedin the prior section. The sensing events involved selected attributes ofa dedicated biodetection device. For example, AFM cantilever tips areconstructed using the same approach and techniques as used devicemanufacturing, the sensor device involving the AFM utilized one ssDNA asa sensing site.

Research Plan to Synthesize a 121 bp DNA Bridge Template:

Step 1. Synthesis of molecule fragments (A+, A−, B+, and B−) withlinkers (small case)

(A+) = 5′-CTGGGCTACACACGTGCTACAATGGACAGAACAAAGGGCAGCGAAACCGCGAGGTTAAGCCAATCC (B+) =5′-CACAAATCTGTTCTCAGTTCGGATCGCAGTCTGCAACTCG ACTGCGTGAAGCTGGgcatg (A−) =3′-tgcaGACCCGATGTGTGCACGATGTTACCTGTCTTGTTTC CCGTCGCTTTGGCGCT (B−) =3′-CCAATTCGGTTAGGGTGTTTAGACAAGAGTCAAGCCTAGCGTCAGACGTTGAGCTGACGCACTTCGACCStep 2. Hybridization of molecule fragments (A+ to A−, and B+ to B−)

(A+/A−) - Heat to 95 Celsius, slow cool to room temperatureCTGGGCTACACACGTGCTACAATGGACAGAACAAAGGGCAGCGAAACCGCGAGGTTAAGCCAATCCtgcaGACCCGATGTGTGCACGATGTTACCTGTCTTGTTTCCCGTCGCTTTGGCGCT (B+/B−) - Heat to 95 Celsius, slow cool to roomtemperature CACAAATCTGTTCTCAGTTCGGATCGCAGTCTGCAACTCGACTGCGTGAAGCTGGgcatgCCAATTCGGTTAGGGTGTTTAGACAAGAGTCAAGCCTAGCGTCAGACGTTGAGCTGACGCACTTCGACCStep 3. Ligate fragments A+/A− to B+/B−

(A+/A−) - In 1x ligation buffer plus T4 DNA ligase at room temperatureCTGGGCTACA----ACCGCGAGGTTAAGCCAATCCCACAAATCTGTT---GTGAAGCTGGgcatgtgcaGACCCGATGT----TGGCGCTCCAATTCGGTTAGGGTGTTTAGACAA---CACTTCGACCThe resulting 121 bp molecules can then be ligated into the Aat II/Sph Icloning sites of pGem-T.

Solutions:

Solution I: 50 mM Glucose (0.9% w/v); 25 mM Tris pH 8, 10 mM EDTA pH 7.5

Solution II: 0.2 N NaOH, 1% SDS

Solution III: 2.7 M potassium acetate to pH 4.8 with glacial aceticacid.SOC Medium=(per 100 ml: 2 grams Bacto®-tryptone (BD), 0.5 grams yeastextract (BD), 1 ml 1 molar NaCl, 0.25 ml 1 molar KCl, 1 ml 2 molar Mg⁺²stock, 1 ml 2 molar glucose)Mg⁺² stock=1 molar MgCl₂, 1 molar MgSO₄

LB/ampicillin/IPTG/X-Gal plates=per liter add 15 grams agar (BD), 10grams Bacto®-tryptone (BD), 5 grams yeast extract (BD), and 5 gramsNaCl; adjust pH with NaOH; autoclave, cool to 50° C.; add ampicillin to100 micrograms per ml, IPTG to 0.5 milimolar, and 80 micrograms permilliliter X-Gal. Pour 30-35 ml of medium per 85 mm plate, let agarharden at 22° C., and store 4° C.

Abbreviations:

ml:millileter, μl:microliter, g:gram, mg:milligram, ng:nanogram, M:molar(moles/liter), mM:millimolar,

(BD=Becton, Dickinson and Company, Franklin Lakes, N.J.) (EM=EMDChemical Inc., Gibbstown, N.J.) (VWR=VWR International, West Chester,Pa.) (Calbiochem/Novabiochm Corp, San Diego, Calif.) (Promega=PromegaCorporation Madison, Wis.) (Pierce=Pierce Biotechnology Inc., Rockford,Ill.)

All chemical and biological detection/identification systems mustincorporate (A) sample collection, (B) sample processing and delivery,(C) sample analysis technology, and (D) signal processing and output(FIG. 1). In one example, the microchip, or series of microchips, iscomposed of thousands of DNA sensitive cantilevers calledmicro-electromechanical systems (MEMS) arranged in a manner to allow forthe detection, identification, and concentration flux of multiplepathogens (multiplex).

Each well on a microchip may contain a single or hundreds ofcantilever-based circuits. Each circuit is composed of some form ofmobile element bridged by preferably a biological molecule such thatwhen the molecule interacts with other molecules, the associated motioncauses the cantilevers to move. Numerous geometries are possible such asa single cantilever suspended over a stage as depicted in the AFMdrawings, a single rotating disc or other shape, or two cantilever armsthat move relative to each other as depicted in FIG. 10. A matrix ofthese bridged cantilevers, or wells of these cantilevers, could beconstructed such that on one axis redundant identical circuits measurethe concentration of a single biological agent depending on the numberof circuits that respond to the presence of the bio-agent. Each row ofthese cantilevers, or wells of these cantilevers, could be dedicated toa different biological agent. Each chip would also contain a significantnumber of reference cantilevers to respond to background levels ofchemical, mechanical, or other environmental ‘noise’. Abiodetection/identification device could include chips that arededicated toward a particular array of biological agents. For example,one device may contain a chip with cantilevers bridged by molecules thatwould only react with agents associated with homeland security. Otherdevices may contain bridged cantilevers that only respond to foodsafety, or agents important to the medical or agricultural industries.

As the biological molecule responds to changes in its environment, themobile elements will deflect, and that subsequent deflection ismeasured. The measurement of motion in MEMS devices is well documented.One way to measure the deformation is to reflect a laser beam off asurface on the deformable element. As the molecule responds, the elementmoves, and the laser beam is subsequently deflected to differentreceptor locations. The change in the reflected beam is measured by thedifferent receptor locations and correlated to the amount of physicalresponse exhibited by the molecule.

The present sensitivities are about 10 angstroms for displacement and 5pico-Newtons for force, but improvements as the size of the deviceshrinks are expected. The smallest transistor-probe structure reportedhas dimensions of 3×2 microns×140 nm. Stanford's Thomas Kenny reportedon the use of slender cantilevers in atomic force microscopes to measureforces at the attonewton (10-18 newton) level.

Several alternate methods for measuring the deformation of the mobileMEMS elements also exist. One method is to include a layer ofpiezoelectric material on the deformable elements themselves. Anotherinvolves adding a mass of magnetic material at the end of a mobile MEMSelement and measuring the change in magnetic field as the mobile elementis moved by the biological element's responses. Yet another involvesmeasuring changes in the capacitance across the gap bridged by thebiological element as it is moved by the biological element.

The mobile elements of the MEMS device shall also comprise a circuit,including the template molecule. Thus, a voltage can be applied acrossthe mobile elements, and a resulting current will pass through thessDNA. The increase in conductivity through the circuit subsequent tohybridization will be measured by sensing the increase in current flow,amplifying that signal and converting the result to digital output forprocessing.

During normal operation, when a sensor site is in its ready state (adetection event has not yet occurred), the voltage across the mobileelements will be set to a “sensing” level. This level is high enough toallow measurable current, but too low to be near the denaturation limit.This current seems to have the additional benefit of drawing targetssDNA to the sensing site, most likely through electrophoresis.

Passing a current through the ssDNA has an additional benefit. Since thessDNA is capable of passing a small amount of current by itself (priorto hybridization), the device has an inherent self-test. If the ssDNAtemplate is damaged, broken, or comes loose from the mobile MEMSelements, the circuit is no longer complete. Thus, the ability of eachsensor site to be in a ready state for a sensing event is able to bevalidated. If a specific site is found to be inoperable, that signalsfrom that site can be removed in software from inclusion in futurecalculations for pathogen presence and concentration calculations.

Having the circuit completed by the template ssDNA will also allow theability to measure the third phenomenon noted earlier: effectingdenaturation using electrical current. The applied voltage can beincreased to a level that results in sufficient current to denature thedsDNA. This provides the sensor with the ability to reset itself, inthat after a sensing event occurs, the pathogen attached to the templateportion of the device can be repelled. The repelled ssDNA target isswept away in the material flowing through the sensor, the voltage islowered back down to its sensing level, and the sensor site is thenready for another sensing event.

The size of these elements is extremely small, such that potentiallythousands of sensor sites could be located on a MEMS chip the size of apenny. Thus, a number of virulence gene regions could be included on agiven chip for a specific pathogen, and additionally, a number ofpathogens could be included on a given chip as well.

In various examples, the sensor of the present subject matter is coupledto a detector. In one example, the detector includes an electricalcircuit and is referred to as a detector circuit. In one example, thedetector utilizes non-electrical means for discerning a physicaldisplacement or resonance condition. In the absence of a modifier, theterm detector includes both electrical and non-electrical detectors.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments, or aspects thereof, may be used in combination with eachother. Many other embodiments will be apparent to those of skill in theart upon reviewing the above description. The scope of the inventionshould, therefore, be determined with reference to the appended claims,along with the full scope of equivalents to which such claims areentitled. In the appended claims, the terms “including” and “in which”are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, or process that includes elements in addition to those listedafter such a term in a claim are still deemed to fall within the scopeof that claim. Moreover, in the following claims, the terms “first,”“second,” and “third,” etc. are used merely as labels, and are notintended to impose numerical requirements on their objects.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, including any cross referenced or relatedpatent or application and any patent application or patent to which thisapplication claims priority or benefit thereof, is hereby incorporatedherein by reference in its entirety unless expressly excluded orotherwise limited. The citation of any document is not an admission thatit is prior art with respect to any invention disclosed or claimedherein or that it alone, or in any combination with any other referenceor references, teaches, suggests or discloses any such invention.Further, to the extent that any meaning or definition of a term in thisdocument conflicts with any meaning or definition of the same term in adocument incorporated by reference, the meaning or definition assignedto that term in this document shall govern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

1. (canceled)
 2. A system comprising: a target molecule introductionport for receiving a sample; a sensor having a template molecule incommunication with the target molecule introduction port and disposedwithin a flow path, the template molecule linked between a first pointon a first surface and a second point on a second surface, the firstsurface independent of the second surface and wherein the templatemolecule has at least one recognition site specific to a targetmolecule, wherein a single stranded conductive nucleic acid molecule isselected as the template molecule; a detector coupled to the first pointand the second point and configured to generate an output signal basedon a change in a measured parameter corresponding to an associationbetween the template molecule with the target molecule, wherein themeasured parameter is electrical conduction through the templatemolecule; and an output circuit to provide a result based on the outputsignal; and wherein the template molecule, the first contact point, thedetector and the second contact point form an electrical circuit, andfurther, wherein the detector comprises a driving circuit for providinga current or voltage through the electrical circuit for disassociationof the template molecule from the target molecule.
 3. The system ofclaim 2 further including a plurality of sensors, each sensor coupled tothe detector by a multiplexer.
 4. The system of claim 2, furthercomprising a processor coupled to the detector and having access to amemory, wherein the memory provides data storage for identifying atarget molecule based on the change in the measured parameter.
 5. Thesystem of claim 2, wherein the output circuit includes at least one ofan interface, a display and a wireless transceiver.
 6. The system ofclaim 2 further including a test circuit coupled to the templatemolecule to determine conductivity of the template molecule.
 7. Thesystem of claim 2 further including a reset circuit coupled to thetemplate molecule to disbond a target molecule from the templatemolecule.
 8. The system of claim 2 further including a housing forcontainment of at least one of the target molecule introduction port,the sensor, the detector and the output circuit.
 9. The system of claim2, wherein an increase in the first physical parameter corresponds to anassociation between the target nucleic acid molecule and the templatenucleic acid molecule.
 10. The system of claim 2, said system comprisingmultiple flow paths in which said sensors are disposed.
 11. The systemof claim 2, said system comprising one or more reservoir.
 12. The systemof claim 2, said system comprising a pumping means.
 13. A methodcomprising: introducing a target molecule into the introduction port ofa system of claim 1 and forming a hybridized nucleic acid molecule;generating an output signal as a function of a change in a firstphysical parameter indicative of electrical conduction through thetemplate molecule disposed in said system, said output signal beingmeasured using the first contact point relative to a reference point,wherein the change in the first physical parameter corresponds to anassociation between the target molecule and the template molecule; andgenerating a current or voltage that passes through the first contactpoint, the template molecule and the second contact point todisassociate the hybridized nucleic acid molecule.
 14. The method ofclaim 13 further including: monitoring a resonant frequency of the firstcontact point relative to a reference point; monitoring a resonantamplitude of the first contact point relative to the reference point;monitoring a distance between the first contact point and the referencepoint; and monitoring an alignment between the first contact point andthe reference point.
 15. The method of claim 14, wherein the referencepoint includes the second contact point.
 16. The method of claim 13,said output signal being selected from impedance, conductivity,resistivity, inductance, and/or capacitance.